State-of-the-Art Zirconia and Glass–Ceramic Materials in Restorative Dentistry: Properties, Clinical Applications, Challenges, and Future Perspectives

Abstract

Ceramic materials have gained outstanding popularity in restorative and prosthetic dentistry due to their combination of high biocompatibility, mechanical durability, and natural esthetics. Among the most important developments in this field are the use of zirconia- and glass-based ceramics for various applications. Zirconia ceramics, especially yttria-stabilized tetragonal zirconia polycrystals (Y-TZP), are famous for their high mechanical strength, transformation toughening, chemical stability, and great biocompatibility. Newer generations like 4Y/5Y-PSZ zirconia have addressed the demand for higher translucency, meeting esthetic requirements. Glass–ceramics, including lithium disilicate and leucite-reinforced systems, are preferred for their optical properties, etchability, and strong adhesive bonding. Their microstructure provides a balance between strength and esthetics, supporting minimally invasive restorations with long-term clinical success. Both zirconia and glass–ceramics exhibit favorable biological responses, including low plaque accumulation and soft tissue compatibility. The goal of ongoing research is to overcome limitations, such as low-temperature degradation, bonding limitations, and surface durability. Also, to improve mechanical performance and functional integration, new approaches include 3D printing, graded materials, nanostructuring, and bioactive coatings. This review aims to provide a comprehensive overview of the composition, properties, clinical applications, current limitations, and future perspectives of zirconia- and glass-based ceramics in restorative dentistry.

1. Introduction

Ceramic materials have gained outstanding popularity in restorative and prosthetic dentistry due to their combination of high biocompatibility, mechanical durability, and natural esthetics. Among the most important developments in this field are the use of zirconia- and glass-based ceramics for various applications. They have also been a great choice for patients who are looking for a safer, metal-free alternative due to potential toxicity and allergies to certain metal alloys [1,2].

Initially, zirconia was introduced as a great alternative to alumina ceramics due to its superior fracture toughness, flexural strength, and reliable performance in load-bearing regions. In the US, full-contour zirconia restorations have been the most popular choice for restorations in the posterior region, largely because of their durability in high occlusal loads [3]. Zirconia-based ceramics, primarily yttria-stabilized tetragonal zirconia polycrystals (Y-ZTP), are widely used in dentistry (i.e., veneers, crowns, bridges, and abutments) due to their mechanical strength, chemical stability, biocompatibility, and optical performance [4]. 3Y-ZTP (zirconia stabilized with 3 mol% Y₂O₃) is the strongest dental ceramic found on the market. Moreover, the increasing demand for esthetics, along with advancements in modern coloring techniques, has further propelled the use of monolithic zirconia in everyday clinical practice. Additionally, zirconia restorations present some benefits. These include requiring less tooth preparation and avoiding issues like veneer chipping that are commonly seen in porcelain-fused-to-zirconia systems [5]. Also, its chemical inertness and low biological reactivity contribute to its excellent biocompatibility, making it a reliable material for long-term intraoral applications. Advancements in surface treatments and digital workflows, such as CAD/CAM, have also expanded zirconia’s functions, improving the clinical outcomes. Additionally, due to its hydrophilic surface, wear and corrosion resistance, antimicrobial action, prevention of plaque buildup, and ability to support periodontal and peri-implant tissue integration, zirconia’s value is reinforced, offering a great alternative to titanium implants, especially in implantology, where they were considered the gold standard [6,7].

Dental glass–ceramics materials were first introduced for restorations in the 1980s as attractive all-ceramic materials that combine the translucency and esthetics of glass with the strength of ceramics. They came as a great alternative to zirconia-based materials, which have a lower translucency, as they have great optical properties (natural-looking translucency and color), good biocompatibility and wear resistance, strong chemical durability, and sufficient mechanical performance for several dental applications [8,9,10,11]. They are manufactured through controlled crystallization of precursor glass, which results in a fine dispersion of crystals within an amorphous matrix. Their unique microstructure provides a mixture of esthetic and bonding advantages. The two primary types used in dental restorations are leucite-reinforced and lithium disilicate ceramics. At present, lithium-disilicate glass ceramics are among the most commonly used, since they are the strongest and toughest. These ceramics have a high volume fraction of interlocking, rod-shaped lithium silicate crystals, which contribute significantly to their superior strength and fracture resistance. Their mechanical performance exceeds that of leucite-reinforced glass ceramics (more than double), making them suitable for a range of applications in the dentistry field, such as crowns, short-span bridges, inlays, and onlays. Due to their lower mechanical performance, leucite-reinforced ceramics are preferred for the anterior region rather than for the posterior crowns and fixed dentures that are subjected to higher masticatory forces [12,13,14].

This review aims to provide a comprehensive and up-to-date synthesis of zirconia- and glass-based dental ceramics by examining their composition, microstructure, mechanical performance, optical and esthetic behavior, biocompatibility, and clinical applications. Although both material classes have been widely studied, most existing literature discusses them separately, leading to a fragmented understanding. To address this gap, the present review consolidates and critically analyzes both zirconia– and glass–ceramic systems, highlighting their respective advantages, limitations, and indication-specific considerations. Furthermore, this review identifies current challenges encountered in both material types, including aging, bonding reliability, optical limitations, and manufacturing constraints, and discusses emerging innovations, such as nanostructured ceramics, graded materials, novel bonding strategies, and advanced fabrication technologies, that aim to overcome these limitations. By integrating established knowledge with recent developments, this work offers a unified perspective intended to guide material selection, clarify clinical decision-making, and support future research in the field of contemporary restorative ceramics.

2. Methodology

This article is a narrative review aimed at synthesizing and critically analyzing up-to-date information on the composition, mechanical and optical properties, biocompatibility, clinical performance, challenges, and future perspectives of zirconia- and glass-based ceramics in restorative dentistry. Relevant studies, technical reports, and clinical guidelines were identified through comprehensive searches conducted in PubMed, Scopus, Web of Science, ScienceDirect, and Google Scholar databases, prioritizing peer-reviewed publications from 1992 to 2025, with special emphasis on studies published after 2020 to capture emerging developments such as nanostructured ceramics, additive manufacturing, graded zirconia systems, and bioactive glass–ceramics. Preference was given to original research articles, systematic reviews, meta-analyses, and clinical trials, while authoritative manufacturer data and specialized textbooks were consulted to supplement information on material composition and processing when peer-reviewed evidence was limited.

Although this work is not a systematic review, the search strategy was developed in accordance with adapted PRISMA principles and applied predefined eligibility criteria to ensure consistency and transparency. Inclusion criteria were as follows: (i) studies published between 1990 and 2025, with priority given to recent literature from the last five years; (ii) articles addressing the composition, structure, mechanical, optical, or biological behavior of zirconia– and glass–ceramic materials used in dental restorations; (iii) studies presenting data on fabrication techniques, clinical applications, or emerging trends such as nano-engineering, ion-releasing systems, and bioactive coatings. Exclusion criteria were as follows: (i) conference abstracts or reports without sufficient methodological detail; (ii) isolated case reports or small case series; (iii) studies unrelated to restorative dentistry or focusing solely on non-dental ceramic applications.

This methodological framework ensures a comprehensive yet focused synthesis of the most relevant and high-quality evidence available, highlighting both historical evolution and recent breakthroughs in zirconia– and glass–ceramic materials. By emphasizing new trends, such as microstructural engineering, hybrid fabrication technologies, and biointeractive surface design. This review seeks to move beyond descriptive reporting toward a critical evaluation of how current innovations address the long-standing trade-offs between strength, translucency, and biological performance in contemporary restorative ceramics.

3. Zirconia-Based Ceramics

3.1. Composition and Structure

Zirconia-based ceramics have become the preferred choice in dentistry, gradually replacing alumina ceramics due to their durability, biocompatibility, and cost-effectiveness [15]. Zirconia (ZrO₂, zirconium dioxide), also known as “ceramic steel”, is a polymorphic ceramic material that is found in three main crystal structures that vary with temperature: (i) monoclinic at room temperature; (ii) tetragonal at approximately 1170 °C; (iii) cubic at temperatures around 2370 °C. During heating or cooling, reversible phase transitions occur, accompanied by volume changes. The most critical is the tetragonal-to-monoclinic (t→m) transformation, which causes a 3–5% expansion that can induce microcracking and degrade mechanical and biological performance in humid conditions. To prevent this, stabilizing oxides such as yttria (Y₂O₃), ceria (CeO₂), magnesia (MgO), calcia (CaO), or alumina (Al₂O₃) are added to control phase stability and minimize internal stresses during cooling [16,17,18]. To stabilize the tetragonal and cubic structures and to prevent undesirable phase transformations during cooling, zirconia is alloyed with aliovalent oxides that substitute for Zr⁴⁺ and create oxygen vacancies, maintaining these high-temperature phases at room temperature. Among these stabilizers, yttria (Y₂O₃) provides the best balance between mechanical strength and fracture resistance [19]. Structural stability also depends on grain size: crystals larger than about 3 µm are prone to spontaneous t→m transformation, whereas fine-grained ceramics with grain sizes below ~0.8 µm retain the tetragonal phase under normal conditions. The average grain size should ideally be around 300 nm to ensure long-term stability in moist oral environments. The classic 3 mol% Y₂O₃ formulation (3Y-TZP), therefore, maintains a fully tetragonal, fine-grained structure capable of resisting crack propagation through transformation toughening [19,20,21].

The same phase change can also occur slowly in moist environments at low temperatures, a phenomenon known as low-temperature degradation (LTD) or aging. During LTD, water molecules penetrate the zirconia lattice and facilitate spontaneous t→m conversion at the surface, causing microcracks, surface uplift, and gradual strength loss over time. Accordingly, key factors such as grain size, yttria distribution, and alumina content must be carefully optimized to harness transformation toughening while minimizing susceptibility to LTD [22,23].

Over the past decade, zirconia has evolved from a single 3Y-TZP formulation into a versatile material platform (3Y/4Y/5Y and >5Y), where the yttria content, residual alumina, and grain size are meticulously controlled to balance optical performance and mechanical strength. Improvements in translucency come from increasing Y₂O₃ content and decreasing Al₂O₃ to ≤0.05 wt%, which enlarges the cubic-phase fraction and reduces light scattering but at the expense of less transformation toughening [20,24,25,26]. Microstructures ranging from cubic-dominant 5Y-PSZ to tetragonal-rich 3Y-TZP have been developed through modern phase engineering, with intermediate 4Y-PSZ providing a strength–translucency compromise. Additionally, recent crystallographic research explains the lower toughness of higher-yttria materials by describing the “non-transformable tetragonal” (t′) phase that cannot undergo stress-induced transformation [27]. Additionally, since 2021, a major innovation has been composition-graded CAD/CAM blanks that combine 3Y→4Y→5Y layers in one disk, yielding a built-in dentin-to-enamel gradient in strength and translucency. The enamel-rich top layer, dominated by cubic ZrO₂, enhances translucency, while the tetragonal base preserves strength. Nevertheless, milling orientation remains critical, as misplacing cubic-rich zones in tension can reduce reliability. Manufacturers have improved granule design and adopted cyclic cold-isostatic pressing to minimize interlayer porosity and achieve more homogenous phase gradients [28,29]. Advances in high-speed and microwave-assisted sintering methods now permit full densification without excessive grain growth, keeping the desired 3Y→5Y gradient. However, deviations from validated cycles can still affect phase balance and translucency. Emerging directions focus on >5Y systems, co-doping with La₂O₃ or CeO₂, and continuous (not layered) compositional gradients to maintain a tetragonal “strength reservoir” beneath cubic, high-translucency surfaces [22,30,31]. For example, it has been shown that adding a small amount of lanthana (~0.2 mol% La₂O₃) to 3Y-TZP significantly improves translucency and hydrothermal stability (aging resistance) through grain-boundary segregation, while retaining excellent mechanical properties [32]. Such co-doping strategies show how new compositions can counteract the usual trade-off between strength and translucency.

In summary, the compositional evolution of zirconia marks a shift from simply preventing phase transformations to intentionally controlling them through targeted microstructural and spatial engineering. These improvements provide more control over translucency, toughness, and stability than ever before, but they also create new trade-offs between optical performance and mechanical reliability. Future advancements in dopant chemistry, gradient design, and hybrid sintering are expected to help mitigate these trade-offs, advancing zirconia towards the next generation of durable and esthetically enhanced dental ceramics.

3.2. Mechanical Properties

Y-ZTP has become essential in restorative dentistry in the past 20 years due to its white color and mechanical properties [15]. 3Y-TZP typically exhibits a flexural strength of 900–1300 MPa, a fracture toughness of 4–10 MPa·m^1/2, and a Vickers hardness of about 12–13 GPa [33,34,35]. Its remarkable performance derives from a transformation toughening mechanism, under stress, metastable tetragonal zirconia grains locally transform to the monoclinic phase, producing a 4–5% volumetric expansion that impedes crack propagation. This phenomenon gives 3Y-TZP excellent high fracture resistance and reliability in load-bearing applications [34]. However, 3Y-TZP is prone to low-temperature degradation (LTD) in humid conditions, as gradual surface transformation can cause microcracking and a progressive decline in strength [35].

To enhance translucency, newer partially stabilized zirconias, such as 4Y-PSZ and 5Y-PSZ (≈4–5 mol% Y₂O₃), incorporate higher cubic-phase content. This optically isotropic phase reduces light scattering and improves esthetics but also lowers strength and toughness due to the diminished transformation-toughening effect. Consequently, 5Y-PSZ usually has a flexural strength of about 500–800 MPa and a fracture toughness of about 4 MPa·m^1/2, which is about 40% lower than 3Y-TZP. However, it has the same hardness and better resistance to hydrothermal aging [36,37]. These trade-offs illustrate how the ongoing shift is from maximizing mechanical strength to customizing phase composition for performance that meets specific needs. For example, 5Y-PSZ is better for front restorations that need to look good, while 3Y-TZP is better for high-load areas [38].

Another important factor is surface quality, which plays a decisive role in zirconia’s mechanical reliability and its interaction with opposing teeth. Well-polished monolithic restorations produce enamel wear comparable to natural enamel, whereas rough or glazed surfaces increase abrasion and stress concentration. Polishing after occlusal adjustment preserves flexural strength, while aggressive grinding without repolishing introduces microcracks that compromise fatigue resistance [39,40]. Clinical and laboratory studies confirm that maintaining a smooth surface is essential for both mechanical longevity and enamel compatibility [39,41,42]. Wet-finishing the pre-sintered zirconia results in greater post-sintering strength compared to dry polishing, attributable to a reduction in introduced flaws, thereby illustrating continuous enhancements in the material’s durability [43].

Additive manufacturing (AM) has changed the mechanical properties of zirconia considerably. It allows more complex geometries, but it also shows that zirconia is denser and stronger than conventionally milled materials. For example, one study reported that a milled 3Y-TZP had a biaxial flexural strength of ~1500 MPa, whereas a printed counterpart (after sintering) reached ~800 MPa under similar conditions [44,45,46]. Recent work also shows that modern 5Y-PSZ, whether machined or printed, experiences no measurable change in phase composition or toughness after accelerated hydrothermal aging, demonstrating that long-term reliability now depends more on microstructural control than fabrication route [47,48]. In terms of wear behavior, preliminary wear simulations indicate that printed zirconia can be made as antagonist-friendly as milled zirconia. For instance, an in vitro chewing simulation showed that robocast (3D-printed) zirconia and uniaxially pressed zirconia caused similar enamel wear on opposing cusps, highlighting that surface finish remains the primary determinant of clinical performance [49].

To improve toughness and fatigue resistance, composite systems such as alumina-toughened zirconia (ATZ) and zirconia-toughened alumina (ZTA) have been re-examined. ATZ, containing ~20 vol% Al₂O₃, combines alumina’s hardness (~18 GPa) with zirconia’s transformation toughening, yielding ~14 GPa hardness and ~8 MPa·m^1/2 toughness, higher than monolithic zirconia but lower than pure alumina [50,51]. ZTA displays the opposite mechanical contrast, gaining toughness but losing hardness as zirconia content increases. Both materials maintain elastic moduli near 300 GPa and superior resistance to slow crack growth, reflecting an evolution from monolithic strength enhancement to fatigue-resistant composite design [51,52,53,54]. In a similar fashion, experimental nano-reinforced zirconias are an emerging research focus. The incorporation of nano-scale fillers (e.g., graphene-based particles) into Y-TZP has demonstrated potential increases in crack resistance and damage tolerance. Graphene-reinforced zirconia composites, for example, have shown improved toughness and Young’s modulus in laboratory tests, without compromising biocompatibility [55]. These early findings suggest that novel nano-toughening strategies might further extend zirconia’s mechanical reliability in the future, although clinical validation is still needed.

Overall, optimizing zirconia’s composition and processing is important to achieve the desired mechanical profile for dental use. Translucency and strength can be balanced to meet anterior or posterior needs by adjusting the stabilizer content (3Y vs. 4Y vs. 5Y) [47,56]. The material’s interaction with the opposing dentition and oral environment is controlled by careful surface treatment (polishing or glazing). New designs are provided by emerging fabrication techniques such as 3D printing. However, for printed zirconia to realize its full mechanical potential, high density and appropriate phase distribution are necessary. Meanwhile, innovations such as functionally graded or bioinspired architectures (e.g., interpenetrating networks or fiber-reinforced zirconia) are being explored to push the boundaries of fracture toughness and fatigue resistance [55]. Because of these ongoing improvements, zirconia-based ceramics are becoming more dependable and stronger for better dental restorations, like layered and graded zirconia and nanotoughened composites [45,47,56,57,58,59]. In summary, the development of zirconia materials in dentistry shows a persistent attempt to strike a balance between the needs for both mechanical integrity and esthetics. Modifications in composition, improvements in manufacturing, and the maximization of surface finishing could propel modern zirconia to offer customized performance.

3.3. Optical Properties and Esthetic Performance

Recently, the focus has been shifting toward natural-looking and durable dental restoration, which has caused an increased attention to improve the optical properties of zirconia-based materials. While zirconia ceramics are known for their excellent mechanical characteristics and biocompatibility, they pose challenges in terms of translucency and fluorescence, particularly in their polycrystalline form [60]. The first generation of zirconia used in dentistry (3Y-ZTP) is well known for its good mechanical properties. However, its optical properties remain a significant limitation. The polycrystalline nature of 3Y-ZTP leads to significant light scattering at grain boundaries and phase interfaces. This results in a white, opaque appearance and limited translucency. In addition, it lacks intrinsic fluorescence, reducing its ability to replicate the optical behavior of natural teeth [60,61]. From a structural and property perspective, these optical deficiencies primarily stem from birefringent tetragonal grains and intergranular defects that redirect and diminish light. Thus, initiatives aimed at enhancing “appearance” must directly involve microstructural control (grain size, phase content, density, and impurity levels) [20]. To overcome these optical limitations, 3Y-ZTP has been veneered with feldspathic ceramics, which offer better translucency, opalescence, and fluorescence. Although this bilayer approach helps improve esthetics, it reduces mechanical capabilities. In particular, the chipping of the veneer layer is due to discrepancies in thermal expansion coefficients and differences in flexural strength between the core and the veneer [20,62].

An effective compromise between strength and balance has been achieved with minimally veneered monolithic zirconia [63]. It is often applied using the cut-back technique, where only the buccal surface is veneered with feldspathic porcelain, while the remainder of the structure remains as monolithic zirconia. This approach maintains the strength of monolithic restorations in occlusal zones while improving optical qualities, such as fluorescence and opalescence on visible surfaces. Clinical outcomes have proven that this method closely mimics the appearance of natural dentition, and at the same time, reduces the risk of veneering layers from chipping [64]. Zirconia lacks the complexity of the light behavior of natural teeth and enamel, and sometimes it appears gray in various lighting. For this reason, efforts are made to bridge this gap by including fluorescein agents, minimal veneering, and customized shading techniques. Manufacturers have also introduced pre-colored and multilayer zirconia blanks with built-in shade gradients to better approximate natural tooth color transitions, reducing the need for external staining [64,65,66,67,68].

As technology advanced, the development of third-generation zirconia, such as 5Y-PSZ, which contains more than 50% cubic phase, has made it possible to address some of the optical and esthetic issues [69]. Because the increased cubic phase content is optically isotropic, it minimizes birefringence and enhances light transmission and translucency. For this reason, 5Y-PSZ represents a better alternative for anterior and esthetically demanding restorations [38,69,70]. However, the same increase in cubic content that improves translucency also eliminates transformation toughening, resulting in a notable reduction in flexural strength [71]. For this reason, 5Y-PSZ is generally recommended for low-stress regions, while tetragonal-rich grades remain more appropriate for posterior load-bearing indications.

To balance these competing needs, architected microstructures made of multilayer or graded-phase zirconias have been developed. These designs place cubic-rich layers facially to make them more translucent, while keeping a tetragonal-dominant core to preserve mechanical resilience. This effectively embeds a “strength core” inside a translucent shell [20,38,62,72]. A complementary innovation involves rare-earth doping to introduce intrinsic fluorescence, a property absent in conventional zirconia. Co-doping translucent Y-TZP with thulium and erbium oxides (~0.8 wt% Tm₂O₃, ~0.5 wt% Er₂O₃) has been shown to reproduce dentin-like fluorescence under UV illumination while maintaining ~1000 MPa flexural strength and tetragonal phase stability [73]. Although it is not yet commercially available, this strategy suggests that fluorescence can be engineered without compromising mechanical performance, offering a new pathway to reduce the flat or grayish appearance of high-translucency zirconia in low-light environments.

Compared to glass–ceramics such as feldspathic porcelain and lithium disilicate, zirconia remains less translucent but significantly stronger [74]. Hybrid materials, such as zirconia-toughened lithium silicate (ZTLS), attempt to bridge this gap [75], and stabilizing agents like Y₂O₃ and La₂O₃ continue to be explored for fine-tuning crystalline phase and optical behavior [76,77]. Additionally, recent work demonstrates that optimized sintering protocols (e.g., higher-temperature vacuum sintering and improved particle packing) can increase the transmittance of 3Y- and 4Y-zirconias by ~30% without compromising strength [20].

Looking forward, two complementary directions appear most promising: (i) processing innovations, including high-temperature densification, advanced isostatic pressing, and surface yttrium enrichment to enhance translucency while maintaining reliability, and (ii) architected microstructures such as multilayer and gradient materials that distribute cubic and tetragonal phases strategically to meet both esthetic and mechanical demands [20,29].

3.4. Biocompatibility

Zirconia is commonly used in crowns, bridges, and implant abutments, among other dental applications, because of its remarkable biocompatibility [23]. In dental implants, it is important to ensure a strong attachment of the gingival tissue to the zirconia material to achieve long-term durability. This is because soft tissue sealing offers protection against bacterial invasion and inflammation, which are common causes of implant failure due to bone loss around the implant [78]. The interaction between zirconia and surrounding tissues depends heavily on the surface morphology and roughness. Surface treatments like sanding and polishing are utilized before clinical use for crowns and abutments to improve biological compatibility and Esthetic outcomes [79,80,81,82]. In some studies, it has been shown that zirconia ceramic materials that have a roughness average lower than 0.1 μm present stronger cell adhesion strength than those that have values higher than 0.1 μm [83,84]. Zirconia has demonstrated a reduced tendency for bacterial adhesion compared to titanium, even at the same surface roughness. Zirconia’s electrical conductivity and surface energy are linked to this decreased bacterial accumulation, which also aids in preventing the formation of biofilms, which can cause complications, such as tooth decay, gingival inflammation, and peri-implant issues during healing [85,86]. Zirconia’s biocompatibility was also supported by studies that have proved its non-cytotoxic nature on both soft and hard tissue-derived cells (fibroblasts and osteoblasts, respectively). Additionally, zirconia enhances osseointegration by promoting osteoblast adhesion, viability, and differentiation, leading to improved bone-implant and long-term implant stability [87,88]. However, these biological interactions are highly dependent on microtopography. Fibroblasts typically exhibit greater adhesion and proliferation on moderately roughened (sandblasted) surfaces, while smoother, polished topographies enhance epithelial cell spreading, indicating that surface design must balance both soft- and hard-tissue integration requirements [89].

Next-generation ultra-translucent, cubic-rich zirconias (4Y/5Y-PSZ and >5 mol% variants) introduce a surface-chemistry dimension to this picture. Relative to 3Y-TZP, their oxide composition typically presents a lower density of surface hydroxyl groups and reduced surface free energy; this can lessen hydrophilicity, blunt early fibronectin adsorption, and slow integrin β3-mediated gingival fibroblast attachment and spreading if the surface is left untreated. To mitigate these effects, targeted conditioning protocols are increasingly applied to restore hydrophilicity and re-establish an adhesive conditioning layer: gentle alumina air-abrasion (to reintroduce controlled micro-roughness without damaging the ceramic), femtosecond-laser micro-texturing (to create stable micro/nanogrooves), and low-pressure/cold-plasma activation (to increase surface oxygen and hydroxyl content and clean hydrocarbons; often described as raising the O/C ratio). These treatments consistently enhance early protein adsorption, focal adhesion formation, and epithelial responses on high-translucency zirconias, bringing peri-implant soft-tissue integration back in line with traditional tetragonal-rich materials. Among these approaches, cold atmospheric plasma (CAP) is notable for modifying surface chemistry without altering micro-roughness. On high-transparency zirconias (e.g., 4Y-PSZ), CAP increases surface oxygen/hydroxyl content (XPS) and markedly lowers the water contact angle (to ~18–19°) while maintaining Ra at approximately 0.05 µm. This promotes early fibronectin adsorption and strengthens integrin β3-linked focal-adhesion signaling (↑FAK, FN, VCL), improving human gingival fibroblast attachment and spreading. In head-to-head tests, post-CAP 4Y-PSZ can show greater HGF responses than 3Y-TZP, with ~30–60 s exposures performing best [90,91,92,93,94,95,96]. Apart from influencing soft-tissue behavior, zirconia also plays a role in modulating immune responses and promoting angiogenesis.

Zirconia’s biocompatibility has also been evaluated using immune cells, such as macrophages, showing no significant cytotoxic effects at concentrations of 10⁷ particles/mL compared to titanium particles [97]. In another study, both 3Y-ZTP and ceria-stabilized zirconia/alumina nanocomposite surfaces enhanced macrophage attachment and growth. They promoted a shift toward the anti-inflammatory M2 phenotype and created an immune environment favorable, which supports the osteogenic process, as marked by the diminished levels of IL-6 and TNF-α (pro-inflammatory markers), and increased levels of IL-10 and TGF-β (anti-inflammatory markers). Moreover, both surfaces promoted osteogenic differentiation and mineralization, as proven by the enhancement of adhesion and proliferation of osteoblasts [98].

Zirconia surfaces have been shown to promote angiogenesis, which is essential for maintaining healthy peri-implant soft tissues. Several studies supported that zirconia promotes vascularization, sustaining soft tissue integration around dental implants. Zirconia-conditioned media have been found to activate endothelial cells’ MAPS/RRK pathways, resulting in epigenetic modifications that promote cell migration, proliferation, and the formation of new vessels [99,100]. In conclusion, zirconia’s superior biocompatibility and advantageous interaction with both soft and hard tissues make it a remarkable material for dental applications. It is especially appropriate for long-term implant success because it can aid in soft tissue sealing, reduce bacterial adhesion, and promote osseointegration. Furthermore, zirconia’s immune-modulating properties and non-cytotoxic nature support its status as a reliable, biologically safe material in contemporary dentistry.

In conclusion, zirconia’s superior biocompatibility and favorable interaction with both soft and hard tissues make it an outstanding material for dental applications. Its ability to facilitate soft tissue sealing, reduce bacterial adhesion, and promote osseointegration is especially advantageous for long-term implant success. Furthermore, zirconia’s immune-friendly properties and lack of cytotoxicity reinforce its status as a safe and reliable biomaterial in contemporary dentistry. It is worth noting that as newer, more translucent zirconias are adopted, surface chemistry optimization becomes as important as topographical tuning. While these cubic-containing formulations might initially bond proteins and cells more slowly due to hydrophobicity, simple chairside treatments like a quick plasma or laser passivation can reactivate their surfaces, ensuring that gingival fibroblasts and epithelial cells attach as readily as they do on traditional 3Y-TZP. This interplay of composition, structure, surface state, and biological response is fundamental to advancing next-generation zirconias and guides current approaches for clinical surface preparation. Additionally, innovative bio-functionalization strategies are on the horizon: for instance, coating zirconia with nano-scale graphene or bioactive glass has been shown in preliminary studies to further improve osteoblast differentiation and antimicrobial properties, potentially marrying zirconia’s mechanical strength with enhanced biological activity [55].

Figure 1 presents a schematic overview of the interplay between composition, structure, mechanical properties, optical/esthetic performance, and biocompatibility in yttria-stabilized zirconia (YSZ) ceramics for dental applications.

3.5. Clinical Applications of Zirconia-Based Ceramics

Zirconia-based ceramics (primarily yttria-stabilized tetragonal zirconia polycrystal, Y-TZP) have become ubiquitous in modern dentistry due to their exceptional qualities, including great mechanical strength, transformation-toughened fracture resistance, and improved optical properties, which have expanded their use across various clinical applications [101]. This subchapter reviews major applications of zirconia in dentistry, emphasizing the unique advantages offered by zirconia’s composition, structure, mechanical properties, optical performance, and biocompatibility.

3.5.1. Veneers

High-translucency monolithic zirconia has recently been introduced for porcelain veneers, including ultra-thin “micro-veneers”. Traditionally, veneers were made from glassy ceramics (like lithium disilicate or feldspathic porcelain) due to their superior translucency and strong resin bondability. Zirconia was long considered too opaque and inert for veneers and was used mainly as a substructure for crowns. But without compromising strength, new zirconia formulations with a higher cubic phase and a lower alumina content have greatly increased [36,37,101,102]. This evolution enables zirconia to be used for ultra-conservative veneers, as thin as ~0.3 mm, luted with minimal or no tooth preparation [36]. Zirconia-based materials present a series of advantages, of which their outstanding mechanical strength. Their flexural strength can be up to ~900–1100 MPa, which far exceeds that of lithium disilicate (~360–400 MPa) [76,103]. In Vitro, zirconia laminate veneers show significantly higher fracture resistance than lithium disilicate or feldspathic porcelain veneers. This allows ultra-thin zirconia veneers to resist cracking during try-in and function, an advantage for brittle glass–ceramics, which often require greater thickness for stability. High strength makes zirconia veneers ideal for bruxism patients or when minimal tooth reduction is desired [36,104]. Another great advantage is that it requires minimal invasive preparations because of its strength. It can be used in micro-veneer form (0.2–0.5 mm) with minimal or no-prep designs. Clinical case reports have demonstrated success with 0.3 mm translucent zirconia veneers, which maintained excellent appearance and did not fracture over 1 year. The ability to preserve enamel is a major benefit, as bonding to enamel improves veneer longevity [36]. A randomized clinical trial evaluated 32 ultrathin zirconia veneers (0.4 mm) over 12 months. During this time, none of the veneers failed, with no fractures or debonding observed. Both the conventional and speed-sintering groups had excellent results, with Alfa ratings for color match, marginal integrity, and surface quality. Also, no occlusal adjustment was needed, and no signs of bruxism were observed after the one-year follow-up. Conventionally sintered veneers demonstrated superior translucency and color integration, making them preferable for higher esthetic demands or if any underlying discoloration must be masked. The study also underlined the importance of a meticulous bonding protocol. Optimal adhesion was achieved using airborne particle abrasion (50 µm alumina at 0.2 MPa), zirconia cleaning gel, and a 10-MDP primer, followed by a translucent light-cured resin cement. Most importantly, zirconia veneers showed excellent biocompatibility and color stability, with ∆E00 values remaining below clinically perceptible thresholds after one year, reinforcing that zirconia is a suitable choice as a strong, esthetic, and conservative option for long-term anterior restorations [105].

While lithium disilicate excels in lifelike translucency, zirconia’s higher opacity can be advantageous for masking dark underlying tooth structure or metal cores [104]. Next-generation “ultra-translucent” zirconia contains ~12 mol% and only 0.1–0.25% alumina (versus ~0.5–1% in conventional 3Y-TZP), increasing cubic phase content and reducing light scattering. Thin sections of these zirconias (~0.3 mm) transmit light well and achieve a pleasant, natural appearance in clinical cases. They remain slightly less translucent than glass ceramics, but this can be beneficial when underlying discoloration must be hidden. In summary, zirconia veneers can provide acceptable esthetics, especially for masking, while avoiding the bulky appearance of traditional porcelain [36,104]. Zirconia is highly biocompatible and inert. It induces minimal gingival irritation and resists plaque accumulation. Patients with metal allergies or sensitivities also appreciate zirconia’s metal-free composition. These features contribute to healthy soft tissue around zirconia veneers [103,106].

However, a significant challenge of zirconia veneers is achieving strong adhesion to the tooth structure. Unlike silica-based ceramics, zirconia cannot be etched with hydrofluoric acid to create a retentive surface (it is acid-resistant and contains no silica). This chemical inertness leads to lower resin bond strength and a risk of debonding if conventional porcelain bonding protocols are used. Numerous surface treatment protocols have been developed to address this issue, such as airborne particle abrasion (sandblasting with alumina to create micromechanical retention), tribochemical silica coating (which adds both mechanical and chemical bonding through silica particles and silanization), and phosphate monomer primers or cements, which form chemical bonds with zirconia’s surface oxides. More recent experimental methods, such as nano-alumina coating, laser texturing, and heat-treated silanes, show promise in improving adhesion, although their long-term clinical performance remains under investigation [36,101]. Based on the evidence, zirconia veneers appear to be a reliable and promising option for anterior restorations. Their strength, minimal preparation requirements, and ongoing clinical success make them a great choice for demanding durability and esthetics, representing a strong, conservative alternative to traditional glass ceramics.

3.5.2. Crowns and Bridges

Zirconia-based ceramics have revolutionized crown and bridge (fixed prosthodontic) restorations in the past two decades. Early zirconia restorations used a bilayer design, a strong Y-TZP core coping veneered with porcelain, as a metal-free alternative to porcelain-fused-to-metal (PFM) crowns. A systematic review investigated 16 clinical studies and found that zirconia-based crowns presented a high 5-year survival of 95–97%. For the implant-supported crowns, the primary failures were due to technical reasons, like fractures within the veneering material. For the tooth-supported crowns, it was reported a mix of both biological and technical complications, including periodontal and endodontic issues, loss of retention, bleeding during probing, and veneering fractures [107].

The primary appeal of zirconia crowns/bridges lies in their exceptional mechanical properties, such as high strength and toughness. Zirconia’s biaxial flexural strength (≥1000 MPa for conventional 3Y-TZP) is about 2–3 times that of high-strength glass–ceramics [104]. Notably, even more translucent zirconia materials like 5Y-TZP retain ~50–60% of the strength of traditional 3Y-TZP, yet remain within or above the typical strength range of other ceramics [101]. Due to their superior mechanical properties, monolithic zirconia crowns require less tooth preparation. In a 5-year clinical study, 40 posterior monolithic zirconia crowns placed by final-year dental students under supervision showed excellent results, with a 95% survival rate and an 85% success rate [108].

Zirconia’s transformation toughening mechanism is a major factor that contributes to its durability. Under stress, metastable tetragonal grains convert to the monoclinic phase with ~5% volume expansion, blunting crack propagation [101]. This process gives zirconia a fracture toughness around 4–10 MPa·m0.5 (for 3Y-TZP), far higher than porcelain or lithium disilicate (≈2–3 MPa·m^0.5) [33,109,110]. As a result, zirconia crowns rarely suffer catastrophic bulk fracture. Even in long-span bridges, zirconia frameworks provide a high margin of safety against crack growth [111].

Because of its great mechanical properties, zirconia restorations have shown promising long-term outcomes in both single and multi-unit applications. A 15-year prospective study involving 562 restorations found failure rates of about 22%, 30%, 37%, and 40% for single crowns, for 2–3-unit bridges, for 4–6-unit spans, respectively, for bridges exceeding 6 units. Still, overall performance at the crown level was encouraging, with approximately 71.7% restorations remaining intact and a relatively low complication rate of approximately 8.5% [112]. Additionally, laboratory and clinical studies underscore zirconia’s robustness. In Vitro tests show that zirconia bridges can withstand forces above 2000 N (well above normal chewing loads), and a systematic review reported nearly 94% survival over a follow-up of at least one year [113].

The shift to monolithic zirconia (full-contour zirconia crowns) has largely solved the chipping problem that affected earlier layered zirconia restorations. Monolithic zirconia crowns demonstrate superior mechanical stability and fewer technical complications than layered metal-ceramic crowns [114]. Five-year studies of monolithic zirconia crowns show survival rates of ~91–98%, comparable to porcelain-fused-to-metal (PFM) crowns, with minimal complications [115]. A prospective trial reported 98% 5-year survival of monolithic zirconia single crowns, with only 6% of crowns having any complication (all minor). In contrast, porcelain-fused PFM crowns often face porcelain chipping or metal framework issues over time [116]. Thus, monolithic zirconia provides a metal-like durability with ceramic esthetics [117].

Traditional 3Y-TZP zirconia is relatively opaque due to light scattering from its fine crystal grains and added alumina. While it is ideal for masking dark stumps, it is less suited for highly esthetic anterior crowns, although it can be indicated for bridges, especially ones of long spans. To address this, new generations of zirconia have improved translucency for better appearance. By increasing yttria content to 4–5 mol% and reducing alumina, manufacturers created high-translucency zirconia with some cubic phase content [36]. These newer zirconias better mimic the brightness of natural teeth. For example, a 5Y-TZP crown can display enhanced translucency, albeit at the cost of some strength (cubic phase is not transformation-toughenable). Multi-layered zirconia blanks go further by integrating layers of varying shade and translucency (dentin layer more opaque/high strength, enamel layer more translucent) to produce a natural color gradient in the crown. Such a graded structure maintains strength in core areas while improving incisal esthetics [101]. With these advances, monolithic zirconia crowns can achieve highly satisfactory esthetics even in anterior regions. One clinical study noted good esthetic results for posterior translucent zirconia crowns, even in cases of limited occlusal space [118]. In summary, while lithium disilicate or porcelain may still edge out zirconia in mimicking the most incisal translucency, the gap has closed markedly. In many clinical scenarios, zirconia offers an acceptable esthetic compromise while providing far greater strength [119,120,121,122,123].

A common concern with ceramic crowns is wear of the opposing dentition. Earlier generation zirconia was extremely hard and often surface-glazed, leading to fears of abrading enamel antagonists [38,41,124]. Stober et al. conducted a 6-month follow-up study on monolithic translucent zirconia crowns placed in molars and found that the wear they caused on opposing teeth was comparable to that caused by other ceramic materials [125]. Key factors in minimizing antagonist wear include avoiding rough glazing (polishing the zirconia instead) and achieving a smooth occlusal surface. With proper finishing, zirconia’s wear behavior is comparable to traditional dental porcelains [41,126].

Additionally, zirconia’s low surface roughness after polishing tends to accumulate less plaque, potentially benefiting periodontal health around crowns. As an inert ceramic, zirconia is highly biocompatible in the oral environment. It does not corrode or release ions, and it has a very low allergenic potential (unlike some base-metal alloys in PFM crowns). Soft tissue response to zirconia crowns is generally excellent, and healthy gingival margins and low inflammation are routinely observed. Some studies suggest that zirconia surfaces accumulate fewer bacteria and plaque than other materials, which could contribute to gingival health. Clinically, patients often report no taste or galvanic sensations with zirconia-based restorations (an occasional issue with metal restorations). All these factors make zirconia crowns especially attractive for patients seeking metal-free, biologically inert dental work [127,128,129,130].

A systematic review of 35 studies found zirconia-based single crowns have a ~98.3% survival rate over ~5 years, which is on par with or even slightly better than metal-ceramic crowns [131]. Ten-year clinical follow-up studies report a zirconia crown survival of approximately 89–93%, indicating good long-term durability. Common complications were rather technical than biological, including primarily chipping, insufficient marginal gaps (up to 50%), debonding (~11%), and occasional secondary caries. No framework fractures were reported. Despite the frequency of these complications, most restorations remained functional, supporting the long-term viability of zirconia-based restorations [132]. In contrast, 10-year results for fully veneered zirconia inlay-retained fixed dental prostheses (a conservative bridge design) showed poorer outcomes. The survival rate was only 12.1% and there was also an increased number of complications, such as veneering ceramic chipping (almost 67%), debonding (~53%), and framework fractures (20%), along with secondary caries and abutment-related problems [133]. Zirconia-based fixed dental prostheses FDPs also show high success. Meta-analysis reported ~95% 5-year survival of posterior zirconia bridges. Even over longer follow-ups (more than 5 years), favorable outcomes are reported with an 85% rate of clinical performance. Importantly, monolithic zirconia FDPs seem to avoid many veneer-related failures, suggesting even better outcomes as more data emerge. Clinical guidance is to use 3Y- or 4Y-TZP for long-span or high-load bridges (due to their higher toughness), and reserve 5Y-TZP for shorter-span or anterior bridges where esthetics are paramount. Monolithic zirconia is now considered a valid alternative to PFM for many cases. For instance, a 2024 systematic review compared implant-supported zirconia crowns to PFM and found both had 97.5–99.1% one-year survival, but zirconia crowns had no ceramic chipping and better mechanical stability (no screw loosening), whereas PFM had multiple veneer chipping incidents (7.61%). A 2022 prospective case series evaluated monolithic zirconia implant-supported single molar crowns with CAD/CAM titanium abutments and revealed a 100% survival rate at one year and an almost 96% success rate per USPHS criteria. Moreover, there were no reported ceramic or abutment fractures, and only two minor complications (4.1% loosening) [117,134,135,136,137]. In conclusion, zirconia crowns and bridges demonstrate excellent long-term clinical performance, comparable or superior to metal ceramics in many cases. Their high survival rates, along with a reduced complication profile and improved esthetics, position them as a reliable and modern choice for crown and bridge restorations.

3.5.3. Orthodontic Applications

Orthodontic brackets made of zirconia represent a newer application of this ceramic, aimed to provide a combination of strength and esthetics in tooth alignment therapy. Esthetic (tooth-colored) brackets have traditionally been made from monocrystalline or polycrystalline alumina ceramics (sapphire or crystalline alumina), which are clear or white and much less visible than metal brackets [138,139,140,141]. Zirconia brackets offer a similar cosmetic advantage but promise improved mechanical performance due to zirconia’s toughness. Researchers have explored zirconia for brackets, especially to overcome the brittleness and slot wear seen in some alumina brackets. Zirconia’s higher fracture toughness makes brackets more resistant to cracking or breakage under orthodontic forces. Recent In Vitro tests of experimental Y-TZP brackets (3Y-, 4Y-, 5Y-zirconia) showed all variants had sufficient fracture strength for clinical use, with 3Y-TZP brackets demonstrating the highest strength and reliability. This suggests zirconia brackets (especially 3Y-based) could better survive debonding forces or accidental impacts that might fracture a standard ceramic bracket. Greater strength also means the bracket can potentially be made smaller or thinner, improving patient comfort and esthetics, without compromising function [4,142,143,144].

CAD/CAM milling of zirconia brackets can achieve very precise slot dimensions and base geometry. Studies have found that zirconia brackets exhibit high manufacturing accuracy (minimal deviation from intended dimensions) due to the fine-grained milling and sintering process. This accuracy ensures a better wire fit and more consistent torque expression and transmission of forces. In contrast, some molded ceramic or plastic brackets may present minor dimensional inconsistencies. Precise slot dimensions in zirconia brackets could translate to more predictable orthodontic movements. Zirconia brackets are color-stable and resistant to staining. In a 2023 study, zirconia brackets were subjected to 20,000 thermocycles and immersion in various dyes. They showed favorable optical stability, with negligible color change. The material’s low porosity and chemical inertness mean that coffee, tea, or other staining agents are unlikely to discolor the brackets over time—a notable benefit over resin brackets (which can stain) or even some alumina brackets that can accumulate pigments in surface defects. Additionally, zirconia’s bright white color can be modified by slight shading to better match tooth enamel, improving on the sometimes chalky-white look of alumina brackets. Overall, patients report high satisfaction with the appearance of zirconia brackets, as they are less visible and do not discolor over the course of treatment [140,144]. Zirconia is tissue-friendly and will not corrode or cause allergic reactions. Many orthodontic patients are adolescents, and metal allergies (e.g., nickel allergy to stainless-steel brackets) can be a concern. Zirconia brackets eliminate that risk. They also tend to have a smoother surface that discourages plaque buildup on the bracket, potentially helping with hygiene around brackets. Gingival health with ceramic brackets is generally good; zirconia’s low plaque affinity may be an added plus [4,138,145,146,147].

A critical aspect of any bracket is the frictional behavior between the bracket, archwire, and ligature, as this affects the efficiency of tooth movement. Studies have shown that currently available zirconia brackets have frictional characteristics very similar to conventional alumina ceramic brackets. In other words, zirconia brackets do not significantly reduce friction compared to other ceramic brackets in sliding mechanics. They produce higher friction than stainless-steel brackets (as do all ceramic brackets) due to their harder, rougher slot surfaces, but manufacturers have attempted to mitigate this (e.g., by polishing the slot or adding a metal slot insert). One approach to address this has been the implementation of hybrid designs. Some ceramic brackets incorporate a stainless-steel slot liner to reduce friction. Pure zirconia brackets without metal slots still show friction on par with alumina brackets, meaning orthodontists must manage friction similarly (sometimes using generous lubrication or early heavier wires to overcome resistance). Nonetheless, the friction is not worse than that of existing esthetic brackets, so zirconia brackets can be used without performance compromise in this regard [138,148].

Bonding of zirconia brackets to teeth is another practical consideration. Because zirconia presents an inert surface and resilience to aggressive chemical agents, it can pose a challenge for bonding [149,150]. However, most ceramic brackets, including zirconia ones, are designed with a special base structure (such as a mechanical retentive pattern or a silica-coated base) to aid bonding. Clinically, the bonding strength of zirconia brackets has been found adequate and comparable to alumina brackets when using appropriate primers and adhesives. If bonding to a zirconia crown or restoration (for patients who need orthodontics with existing zirconia restorations), the same special primers (10-MDP or tribochemical coating) would be indicated. For bonding zirconia brackets to natural enamel, standard etching and a good orthodontic adhesive are generally sufficient, since the bracket base is pretreated by the manufacturer. Additional primers are optional but may enhance bond reliability [150,151,152,153].

In summary, zirconia orthodontic brackets combine excellent esthetics with robust mechanical properties. They represent a promising alternative for patients who desire invisible braces without compromising on strength. While frictional forces are not reduced compared to classic ceramic brackets, the overall treatment seems to be just as effective.

3.5.4. Implants

Zirconia dental implants are typically one-piece or two-piece screws made from Y-TZP ceramic, intended to integrate with bone similarly to titanium implants. They were developed to fulfill patient demands for metal-free solutions and to prevent any gray shine-through in thin gingiva. Modern zirconia implants are often ivory-white in color, mimicking the natural tooth root hue and offering superb esthetics in the gingival area [154,155,156]. Initial outcomes for zirconia implants have been positive. Zirconia is bioinert but supports osseointegration when its surface is appropriately roughened. Studies show that rough-surfaced zirconia implants achieve bone-to-implant contact ratios comparable to titanium [157,158]. In fact, modified zirconia surfaces (created by sandblasting, acid-etching, laser micro-grooving, or selective infiltration) can demonstrate faster initial osseointegration than smooth titanium, thanks to increased surface energy and wettability. For instance, laser-created microgrooves (2 μm width) on zirconia have been shown to significantly enhance new bone formation and interfacial strength. While each manufacturer’s surface differs, common approaches include grit-blasting zirconia with alumina and/or acid etching it, yielding a moderately rough topography that is conducive to bone cell attachment. As a result, zirconia implants can achieve stability and bone integration at levels essentially on par with titanium implants [159,160].

A systematic review and meta-analysis found that after 1 year of function, zirconia implants had survival rates statistically similar to titanium implants, with success rates of ~58–93% for zirconia implants and 57–100% for the titanium ones [161]. Commercially available zirconia implants have shown reliable performance after 5 years, with a high survival rate (~95%) and stable marginal bone loss [159]. An additional benefit of zirconia implants is their positive interaction with surrounding soft tissues. Zirconia tends to accumulate less plaque and exhibit lower inflammation in peri-implant tissues. Some clinical trials reported higher pink esthetic scores (PES) for zirconia implants, meaning better gingival color and contour outcomes compared to titanium [161]. One reason is that the white implant core does not show through the gingiva or cause a grayish hue. Also, since zirconia does not corrode, there are no metal ions that could potentially induce localized discoloration or inflammatory reactions. From an esthetic standpoint, in the anterior zone, zirconia implants can yield superior results. Case reports describe stable, healthy, and pink gingiva around zirconia implant crowns, with no gray shadow in the cervical area (a common challenge with titanium in thin gingival biotypes). This makes zirconia implants ideal for cosmetically sensitive areas [106,156,162,163,164,165,166].

Zirconia implants were historically introduced as one-piece designs (implant and abutment in one, requiring transmucosal healing). This avoids a metal interface but does limit some flexibility in angulation and requires careful surgical placement. One-piece zirconia implants show success in studies conducted over a period of 5 years, with about 95–98% survival rates and success rates of 91% [167,168].

Newer two-piece zirconia implant systems have emerged, featuring either a ceramic screw or a carbon-fiber tie screw, or a metal insert to connect a zirconia abutment. These aim to mirror the versatility of two-piece titanium systems. Mechanical testing indicates that while zirconia implants are extremely strong in compression, they can be more susceptible to bending or tensile forces (being a brittle material). The elastic modulus of zirconia (200–210 GPa) is about double that of titanium (~110 GPa), making zirconia implants very stiff [169,170,171]. This theoretically could concentrate stress in bone (less elastic accommodation), but clinically, no adverse bone response has been observed due to stiffness alone. To mitigate fracture risk, manufacturers often increase zirconia implant diameter or optimize thread geometry [170,171,172].

In summary, zirconia implants are proving to be a viable alternative to titanium, especially appreciated in patients demanding superior esthetics or metal-free reconstruction. They demonstrate good survival and success even over longer periods and can achieve strong osseointegration.

3.5.5. Abutments

Even when titanium implants are used, zirconia finds important applications in the prosthodontic phase of implant therapy. Notably, zirconia abutments (the intermediate piece that connects the implant to the crown) have become extremely popular. These abutments are either a one-piece (monolithic) component that screws directly into an implant or a two-piece in which a zirconia sleeve is bonded to a titanium base (Ti-base hybrid abutment) [173,174,175]. A zirconia abutment will not shine through or darken the peri-implant mucosa, unlike a metal abutment, which can impart a grayish color, especially in thin mucosa [173]. Soft tissue appears to adhere well to zirconia abutment surfaces, with a stable epithelial attachment and low inflammation. Moreover, zirconia abutments present less plaque accumulation compared to titanium, and in experimental mucositis conditions, they have shown significantly lower plaque and bleeding scores [176,177,178]. Additionally, they are well tolerated by patients with metal sensitivities and are not known to provoke allergic reactions [179]. The downside of zirconia abutments is their reduced mechanical resilience compared to metal. Titanium abutments have higher fracture/bending strength than zirconia [38,180]. Long-span or angled zirconia abutments under heavy load have, in some cases, fractured at the screw or the collar. To address this, zirconia abutments are mostly used in anterior or premolar regions (lower stress), and titanium or hybrid abutments are used in molar regions. Another strategy is the Ti-base approach: a short titanium interface provides ductility and strength where the abutment meets the implant, while the outer form is zirconia for esthetics. This hybrid has shown very good success, effectively eliminating abutment fractures in practice [180,181,182,183,184,185].

Thakare et al. evaluated in a review the clinical performance of zirconia abutments compared to titanium ones and submucosal modified zirconia abutments with pink glass ceramic. Zirconia abutments were shown to offer superior esthetic results, especially in patients with thin gingival phenotypes, due to their favorable light transmission and reduced risk of mucosal discoloration. However, the esthetic benefit observed when zirconia abutments were veneered with pink ceramic was unfavorable at the peri-implant level due to the grayish discoloration it creates. Biological outcomes were not statistically significant between the groups. However, long-term data indicated that titanium implants presented a higher marginal plaque accumulation. Zirconia abutments had a reduced mid-buccal pocket depth over time, likely due to better soft tissue adaptation and biological sealing. In contrast, veneered zirconia abutments had rougher surfaces, which led to increased plaque, deeper pockets, more bleeding, and a greater risk of bacterial colonization linked to peri-implantitis. Mechanically, titanium abutments demonstrated 100% survival and no fractures, while zirconia abutments had a slightly lower survival rate of 94.4%, with some fractures occurring mostly in internally connected designs and in the posterior region. Overall, zirconia abutments represent a good esthetic choice in anterior and premolar areas, especially with thin gingiva. However, more RCTs are needed to evaluate their reliability in high-stress posterior restorations [185]. A systematic review and meta-analysis evaluated clinical outcomes of zirconia dental implants based on 25 studies, including 4017 implants placed in 2083 patients. The results showed a high 10-year cumulative survival rate of about 95%. Most failures occurred within the first year after implantation. Implant fractures made up 15.1% of the 172 failures, representing only 0.65% of all implants (comparable to titanium with 0.44% failures), mostly being in narrow-diameter and already discontinued models. One-piece implants had significantly better survival rates than two-piece designs, making zirconia a promising metal-free alternative [186]. A 5-year randomized controlled clinical study compared cemented (CR) and screw retained (SR) zirconia-based single crowns supported by zirconia abutments on two-piece implants placed in the esthetic zone. A total of 44 patients were included, with a follow-up period of 5 years. The overall implant survival rate was 95.5%, with a 100% survival in the SR group and 90% in the CR group. Restoration survival was lower (81.2%), due to abutment fractures, which occurred in both groups, but slightly more often in the SR group. Technical complications included abutment fractures, ceramic chipping (more frequent in CR), and screw loosening (only in CR), reported in 29.3% cases. Biological complications occurred exclusively in the CR group (36.8%), including peri-implant mucositis and two implant losses. Marginal bone levels remained stable in both groups, with no significant differences. Based on these findings, zirconia abutments supporting screw-retained crowns demonstrate significantly fewer complications. This makes screw-retained zirconia-based restorations a more favorable option over time, due to reduced risk of biological problems associated with excess cement [22]. In summary, zirconia abutments represent a great alternative for the anterior (especially) and premolar regions. Although they have lower mechanical strength than titanium, this limitation could be addressed by using Ti-based hybrid designs.

Table 1 presents an overview of the main clinical uses of zirconia, including the type and number of restorations tested, evidence level, follow-up duration, anatomical location, survival and complication rates, and the nature of complications encountered, as well as study limitations.

Table 1. A summarization of zirconia-based dental materials’ clinical applications.

Type of Restoration	Material	Study Type	EV	No. of Samples Tested	Follow-Up Duration	Tested Location	Survival Rate	Complication Rate (Annual/Cumulative)	Study Limitations	Type of Complications	Ref
Veneers	Monolithic cubic ultra-translucent zirconia	Case Report	V	6	1 year	Anterior	NR (all restorations intact)	0% (cumulative)	Single case-level; short follow-up; protocol not standardized	-	[36]
Laminate Veneers	Ultrathin translucent zirconia (conventional sintered vs. speed sintered zirconia)	RCT	II	32	1 year	Anterior, Posterior	NR (all intact)	18.75% (conventional sintering), 25% (speed sintering) (cumulative)	Short follow-up; color endpoint only; bonding not uniform	Marginal discoloration	[105]
Veneers	Multi-shaded translucent zirconia	Split-mouth RCT	II	15	5 years	Anterior	93.3%	6.67% (cumulative)	Small sample; veneer thickness/adhesion details NR	-	[187]
Minimally invasive veneers	Monolithic ultratranslucent zirconia	Case series	IV	28	4.33 years	-	100%	3.57% (cumulative)	No control; bonding protocol may vary	Superficial marginal discoloration in the maxillary left lateral incisor	[188]
Veneers (3D gel deposition)	Self-glazed zirconia (3Y-ZTP)	Retrospective	III	45	37 months	Anterior, Posterior	100%	4.4% (cumulative)	No control; finishing unique (self-glazed), generalizability limited	Yellowish color change after cementation	[189]
Single-unit ceramic laminate veneers	Translucent zirconia veneers etched with hydrofluoric–nitric acid mixture and bonded with MDP-containing polymeric adhesive	Double-blind RCT	II	26	1 year	Anterior, Posterior	100%	3.8% (cumulative)	Short follow-up; aggressive surface Protocol (not routine)	Debonding	[102]
Tooth-supported crowns	Zirconia-based	SR	I	-	Up to 5 years	-	95.9%	-	Pooled designs; zirconia generations mixed; outcomes heterogeneous	Veneering material fractures, bleeding on probing, loss of retention, and endodontic treatments	[107]
Implant-supported crowns	Zirconia-based	SR	I	-	Up to 5 years	-	97.1%	-	Pooled implant systems; veneer/monolithic mixed	Veneering material fractures, bleeding on probing	[107]
Crowns	Monolithic Zirconia	Prospective	III	40	5 years	Posterior	95%	15% (cumulative)	Student operators; finishing varies; parafunction NR	Color mismatch (5%), surface roughness (5%), marginal integrity issues, such as gap or exposure with secondary caries (5%), anatomical shape change (2.5%), and crown fracture (2.5%).	[103]
Single crowns	Zirconia cores veneered with feldspathic porcelain.	Prospective observational	III	192	15 years	Anterior, Posterior	77.6%	~4.8% (cumulative)	Long follow-up; veneering liability prominent	Veneer fracture (5.01%), loss of retention (14.85%), crown loss due to extraction (1.73%)	[89]
Fixed Partial Denture (FPD)—Bridges	Zirconia cores veneered with feldspathic porcelain.	Prospective observational	III	370 crowns (in bridges: 2–3, 4–6, >6 units)	15 years	Anterior, Posterior	62.96%	~4.8% (cumulative)	Long spans; connector/veneer risks accumulate	Veneer fracture (5.01%), loss of retention (14.85%), crown loss due to extraction (1.73%)	[112]
Crowns	Monolithic zirconia	Clinical observational	III	209	3 years	Anterior, Posterior	91.5%	21.5% (cumulative)	Endpoints broad; risk factors NR	Sensitivity/pain (8.7%), occlusal adjustment (4.1%), periodontitis (5.6%), recurrent caries (2.1%), crown recementation (2.6%), infections (2.1%), irreversible pulpitis (2.1%), open margins (1.0%), loose crown/tooth (3.1%), endodontic issues (2.0%), and porcelain repair (0.5%).	[115]
Crowns	Monolithic 3Y-TZP zirconia	Prospective	III	50	5 years	Posterior	98%	6% (cumulative)	Small cohort; parafunction control NR	Debonding (4%), root fracture (2%)	[116]
Crowns	Monolithic zirconia	SR/MA of RCTs	I	86	1 year	Posterior	97.5%	3.33% (annual)	RCTs pooled; short horizon; bruxism often excluded	Chipping due to bruxism (1.1%), screw-loosening (2.82%), implant failure (1.6%)	[117]
Zirconia single crowns (SCs)	Zirconia-ceramic (veneered)	SR/MA	I	952	3.8 years	Anterior, Posterior	96.3%	4.5% (annual)	Veneer chipping, screw loosening prominent	Ceramic chipping (1.84%), ceramic fractures (0.98%), core fractures (0.17%), catastrophic veneer fractures (0.71%), abutment fractures (0.23%), screw loosening (0.53%), loss of retention (0.20%), soft tissue complications (2.73%), and bone loss >2 mm (0.31%).	[131]
Zirconia SCs	Monolithic zirconia	SR/MA	I	394	1.6 years	Anterior, Posterior	96.1%	3.6% (annual)	Short mean follow-up; low veneer-related events	Ceramic chipping (0.39%), ceramic fractures (0.58%), catastrophic veneer fractures (0.19%), abutment fractures (0.39%), screw loosening (2.27%), loss of retention (4.55%), soft tissue complications (3.9%), and bone loss >2 mm (1%).	[131]
SCs	Veneered zirconia	Clinical observational	III	28	10 years	-	92.9%	54% technical, 12% biological (cumulative)	Veneer/fit liabilities explicit; small sample	Chipping (50%), marginal gap issues (50%), mild periodontal issues	[132]
FPDs	Veneered zirconia framework	Clinical observational	III	57	5 years	Posterior (3- and 5-unit bridges)	73.9%	26.1% (cumulative)	Connector/veneer sensitivity; trauma event reported	21.7% secondary caries, 15.2% ceramic chipping, 1 framework fracture due to trauma	[144]
FPDs	Veneered zirconia frameworks	SR	I	423	Up to 10 years	Posterior	84.35%	~35–40% (cumulative)	Veneer chipping up to 32%; marginal & retention issues	Chipping of the veneering ceramic (up to 32%), loss of retention (~5%), framework fractures (~4.5%), marginal discrepancies (~16.7–90.7%), secondary caries (~7.9%), endodontic issues (~10.9%), and abutment tooth fractures (~2.2%)	[137]
Cantilever RBFDP (anterior bridge)	Zirconia ceramic	Clinical observational	III	108	10 years	Anterior	98.2%	6.5% (cumulative)	Strong performance in the conservative anterior span	Debonding (5.6%), chipping (0.9%)	[190]
Cantilever RBFDP (anterior bridge)	Zirconia-based	Clinical observational	III	24	up to 61 months	Anterior	100% at 36 months	~17.6% (cumulative)	Small series; debonding & chipping modest	Debonding (4.2%), incisal chippings (8.3%), orthodontic relapse (4.2%)	[191]
Inlay-Retained Fixed Dental Prosthesis (IRFDP)	Zirconia (Vita In-Ceram YZ), veneered with feldspathic porcelain	Clinical observational	III	30	5 years	Posterior	95.8%	16.7% (cumulative)	Bonding-dependent; chipping/debonding present	Debonding (6.9%), chipping (10.5%), secondary caries (8.1%)	[192]
3-/4-Unit Posterior FDPs (conventional)	Zirconia (Cercon Smart Ceramics, Charlotte, NC, USA), veneered (first-gen CAD/CAM)	Prospective	III	99	10 years	Posterior	75%	60% (cumulative)	First-gen CAD/CAM; veneer liability high	Absolute technical failures (13.1%), such as framework fractures and chipping, and relative failures requiring clinical intervention (50.5%), of which 35.4% were due to technical issues.	[193]
Dental Implant-supported prostheses, including SCs (85%), FDPs (9.6%), overdentures (5.4%)	Y-TZP, ATZ	SR/MA	I	4017	10 years	Anterior, Posterior	95.1%	4.3% (cumulative)	Older/discontinued systems included; narrow-diameter risk flagged	Fractures (0.65%, especially in narrow-diameter implants—3.25 mm—with 69% of fractures from Z-Look3), early failures before osseointegration (~41% of analyzed failures), mechanical weakness from drill-preparation (7.5% failure rate vs. 3.5% for non-prepared), material aging of Y-TZP, and higher failure rates in discontinued or prototype systems (11.3% vs. 2.5% for commercially available implants).	[160]
Dental Implant-supported prostheses, including SCs	One-piece zirconia dental implants (CeraRoot, Santa Monica, CA, USA) featuring three distinct roughened surface treatments: coated, uncoated, and acid-etched.	Comparative observational	III	831	5 years	-	95% (92.77% for uncoated implants, 93.57% for coated implants, and 97.60% for acid-etched implants)	-	Surface variants pooled; center effects	-	[166]
Dental implant-supported prostheses, including SCs (two-piece implant)	Zirconia implants (ZERAMEX® T, ZrO2-ATZ-Bio-HIP, Spreitenbach, Switzerland)	Prospective	III	76	Up to 3 years	Posterior	87.3% (2-year) 85% (3-year cumulative)	4% (cumulative)	Early gen; aseptic loosening notable	Aseptic loosening (13%), abutment fracture (2.6%)	[127]
Implant-supported fixed complete dentures (Zir-IFCDs)	Zirconia	Retrospective cohort	III	67	5 years	Anterior, Posterior	70.9%	13.4% (cumulative)	Framework fractures in a limited restorative space	Framework fracture (4.4%), all associated with limited vertical restorative space, veneering porcelain fracture (1.5%), implant loss (3.0%), esthetic concerns (3.0%), and one failure of unknown cause (1.5%)	[194]
Implant-supported prostheses, including SCs and 3-unit FDPs	ATZ implants	ProspectCohort	III	53	5 years	Anterior, Posterior	94.3%	8.3% (cumulative)	MBL > 2 mm endpoint	Marginal bone loss > 2	[195]
Dental implant-supported prostheses, including single-tooth replacements	Zirconia	Prospective	III	30	5 years	Anterior, Posterior	93.3%	40% (cumulative)	Small cohort; maintenance factors	peri-implant mucositis (26.7%), peri-implantitis, and implant failure (6.7%)	[196]
Dental implant-supported prostheses, including SCs and 3-unit FDPs—one-piece zirconia implants	Zirconia	Prospective Cohort	III	71	5 years	Anterior, Posterior	98.4%	1.6% (cumulative)	Good survival; details of hygiene protocols NR	Implant failure (0.7 mm), but stable thereafter	[197]
Dental implant-supported prostheses, including SCs— one-piece implant	Y-TZP (zirconia) with a ZiUnite® surface (Nobel Biocare, Zürich, Switzerland).	Prospective Cohort	III	66	5 years	Anterior, Posterior	78.2%	27% (cumulative)	Higher peri-implantitis/MBL; system-specific	Implant failure (21.2%), peri-implantitis (21.2%), marginal bone loss >2 mm (27%), and implant fracture (1.5%).	[198]
Abutments— Implant-supported SCs with zirconia abutments. Implant Type: Standard Platform (SP) vs. Platform Switching (PS)	Zirconia abutments	Retrospective	III	158	Up to 12 years	Anterior	SP (93.8.%) up to 12 years, PS (90%) up to 5 years	10.1% (cumulative)	Platform/MBL differences; soft-tissue endpoints	Abutment fractures (1.9%) loss of retention (frequency not specified) and marginal bone loss, which was more pronounced in standard platform designs compared to platform-switching designs	[199]
Abutments (two-piece)	Zirconia	Retrospective	III	32	6 years	Anterior, Posterior	100%	21.9% (cumulative)	Screw loosening/chips; small cohort	Abutment screw loosening (3.1%), veneering ceramic chipping (6.2%), crown loosening or decementation (9.3%), and occlusal roughness (3.1%)	[200]
Single-tooth implants supporting veneered porcelain crowns, using zirconia abutments	Zirconia abutments with porcelain veneer	Retrospective	III	29	10 years	Anterior, Posterior	97.9%	~41.4% (cumulative)	Mucositis prevalent; veneer chip & screw issues	Peri-implant mucositis (34.5%), veneering porcelain chipping (6.9%), and abutment screw loosening (6.9%)	[178,201]
Implant-supported single crowns with zirconia abutments	Zirconia abutments	MA	I	429	Up to 5 years	Anterior, Posterior	39.4%	-	Heterogeneous definitions; esthetic outcomes favorable vs. Ti/Au	Low marginal bone loss, least soft tissue discoloration (vs Ti & Au)	[202]

Abbreviations: EV, evidence level; SR/MA, systematic review/meta-analysis; RCT, randomized controlled trial; SC, single crown; NR, not reported.

Table 1. A summarization of zirconia-based dental materials’ clinical applications.

Type of Restoration	Material	Study Type	EV	No. of Samples Tested	Follow-Up Duration	Tested Location	Survival Rate	Complication Rate (Annual/Cumulative)	Study Limitations	Type of Complications	Ref
Veneers	Monolithic cubic ultra-translucent zirconia	Case Report	V	6	1 year	Anterior	NR (all restorations intact)	0% (cumulative)	Single case-level; short follow-up; protocol not standardized	-	[36]
Laminate Veneers	Ultrathin translucent zirconia (conventional sintered vs. speed sintered zirconia)	RCT	II	32	1 year	Anterior, Posterior	NR (all intact)	18.75% (conventional sintering), 25% (speed sintering) (cumulative)	Short follow-up; color endpoint only; bonding not uniform	Marginal discoloration	[105]
Veneers	Multi-shaded translucent zirconia	Split-mouth RCT	II	15	5 years	Anterior	93.3%	6.67% (cumulative)	Small sample; veneer thickness/adhesion details NR	-	[187]
Minimally invasive veneers	Monolithic ultratranslucent zirconia	Case series	IV	28	4.33 years	-	100%	3.57% (cumulative)	No control; bonding protocol may vary	Superficial marginal discoloration in the maxillary left lateral incisor	[188]
Veneers (3D gel deposition)	Self-glazed zirconia (3Y-ZTP)	Retrospective	III	45	37 months	Anterior, Posterior	100%	4.4% (cumulative)	No control; finishing unique (self-glazed), generalizability limited	Yellowish color change after cementation	[189]
Single-unit ceramic laminate veneers	Translucent zirconia veneers etched with hydrofluoric–nitric acid mixture and bonded with MDP-containing polymeric adhesive	Double-blind RCT	II	26	1 year	Anterior, Posterior	100%	3.8% (cumulative)	Short follow-up; aggressive surface Protocol (not routine)	Debonding	[102]
Tooth-supported crowns	Zirconia-based	SR	I	-	Up to 5 years	-	95.9%	-	Pooled designs; zirconia generations mixed; outcomes heterogeneous	Veneering material fractures, bleeding on probing, loss of retention, and endodontic treatments	[107]
Implant-supported crowns	Zirconia-based	SR	I	-	Up to 5 years	-	97.1%	-	Pooled implant systems; veneer/monolithic mixed	Veneering material fractures, bleeding on probing	[107]
Crowns	Monolithic Zirconia	Prospective	III	40	5 years	Posterior	95%	15% (cumulative)	Student operators; finishing varies; parafunction NR	Color mismatch (5%), surface roughness (5%), marginal integrity issues, such as gap or exposure with secondary caries (5%), anatomical shape change (2.5%), and crown fracture (2.5%).	[103]
Single crowns	Zirconia cores veneered with feldspathic porcelain.	Prospective observational	III	192	15 years	Anterior, Posterior	77.6%	~4.8% (cumulative)	Long follow-up; veneering liability prominent	Veneer fracture (5.01%), loss of retention (14.85%), crown loss due to extraction (1.73%)	[89]
Fixed Partial Denture (FPD)—Bridges	Zirconia cores veneered with feldspathic porcelain.	Prospective observational	III	370 crowns (in bridges: 2–3, 4–6, >6 units)	15 years	Anterior, Posterior	62.96%	~4.8% (cumulative)	Long spans; connector/veneer risks accumulate	Veneer fracture (5.01%), loss of retention (14.85%), crown loss due to extraction (1.73%)	[112]
Crowns	Monolithic zirconia	Clinical observational	III	209	3 years	Anterior, Posterior	91.5%	21.5% (cumulative)	Endpoints broad; risk factors NR	Sensitivity/pain (8.7%), occlusal adjustment (4.1%), periodontitis (5.6%), recurrent caries (2.1%), crown recementation (2.6%), infections (2.1%), irreversible pulpitis (2.1%), open margins (1.0%), loose crown/tooth (3.1%), endodontic issues (2.0%), and porcelain repair (0.5%).	[115]
Crowns	Monolithic 3Y-TZP zirconia	Prospective	III	50	5 years	Posterior	98%	6% (cumulative)	Small cohort; parafunction control NR	Debonding (4%), root fracture (2%)	[116]
Crowns	Monolithic zirconia	SR/MA of RCTs	I	86	1 year	Posterior	97.5%	3.33% (annual)	RCTs pooled; short horizon; bruxism often excluded	Chipping due to bruxism (1.1%), screw-loosening (2.82%), implant failure (1.6%)	[117]
Zirconia single crowns (SCs)	Zirconia-ceramic (veneered)	SR/MA	I	952	3.8 years	Anterior, Posterior	96.3%	4.5% (annual)	Veneer chipping, screw loosening prominent	Ceramic chipping (1.84%), ceramic fractures (0.98%), core fractures (0.17%), catastrophic veneer fractures (0.71%), abutment fractures (0.23%), screw loosening (0.53%), loss of retention (0.20%), soft tissue complications (2.73%), and bone loss >2 mm (0.31%).	[131]
Zirconia SCs	Monolithic zirconia	SR/MA	I	394	1.6 years	Anterior, Posterior	96.1%	3.6% (annual)	Short mean follow-up; low veneer-related events	Ceramic chipping (0.39%), ceramic fractures (0.58%), catastrophic veneer fractures (0.19%), abutment fractures (0.39%), screw loosening (2.27%), loss of retention (4.55%), soft tissue complications (3.9%), and bone loss >2 mm (1%).	[131]
SCs	Veneered zirconia	Clinical observational	III	28	10 years	-	92.9%	54% technical, 12% biological (cumulative)	Veneer/fit liabilities explicit; small sample	Chipping (50%), marginal gap issues (50%), mild periodontal issues	[132]
FPDs	Veneered zirconia framework	Clinical observational	III	57	5 years	Posterior (3- and 5-unit bridges)	73.9%	26.1% (cumulative)	Connector/veneer sensitivity; trauma event reported	21.7% secondary caries, 15.2% ceramic chipping, 1 framework fracture due to trauma	[144]
FPDs	Veneered zirconia frameworks	SR	I	423	Up to 10 years	Posterior	84.35%	~35–40% (cumulative)	Veneer chipping up to 32%; marginal & retention issues	Chipping of the veneering ceramic (up to 32%), loss of retention (~5%), framework fractures (~4.5%), marginal discrepancies (~16.7–90.7%), secondary caries (~7.9%), endodontic issues (~10.9%), and abutment tooth fractures (~2.2%)	[137]
Cantilever RBFDP (anterior bridge)	Zirconia ceramic	Clinical observational	III	108	10 years	Anterior	98.2%	6.5% (cumulative)	Strong performance in the conservative anterior span	Debonding (5.6%), chipping (0.9%)	[190]
Cantilever RBFDP (anterior bridge)	Zirconia-based	Clinical observational	III	24	up to 61 months	Anterior	100% at 36 months	~17.6% (cumulative)	Small series; debonding & chipping modest	Debonding (4.2%), incisal chippings (8.3%), orthodontic relapse (4.2%)	[191]
Inlay-Retained Fixed Dental Prosthesis (IRFDP)	Zirconia (Vita In-Ceram YZ), veneered with feldspathic porcelain	Clinical observational	III	30	5 years	Posterior	95.8%	16.7% (cumulative)	Bonding-dependent; chipping/debonding present	Debonding (6.9%), chipping (10.5%), secondary caries (8.1%)	[192]
3-/4-Unit Posterior FDPs (conventional)	Zirconia (Cercon Smart Ceramics, Charlotte, NC, USA), veneered (first-gen CAD/CAM)	Prospective	III	99	10 years	Posterior	75%	60% (cumulative)	First-gen CAD/CAM; veneer liability high	Absolute technical failures (13.1%), such as framework fractures and chipping, and relative failures requiring clinical intervention (50.5%), of which 35.4% were due to technical issues.	[193]
Dental Implant-supported prostheses, including SCs (85%), FDPs (9.6%), overdentures (5.4%)	Y-TZP, ATZ	SR/MA	I	4017	10 years	Anterior, Posterior	95.1%	4.3% (cumulative)	Older/discontinued systems included; narrow-diameter risk flagged	Fractures (0.65%, especially in narrow-diameter implants—3.25 mm—with 69% of fractures from Z-Look3), early failures before osseointegration (~41% of analyzed failures), mechanical weakness from drill-preparation (7.5% failure rate vs. 3.5% for non-prepared), material aging of Y-TZP, and higher failure rates in discontinued or prototype systems (11.3% vs. 2.5% for commercially available implants).	[160]
Dental Implant-supported prostheses, including SCs	One-piece zirconia dental implants (CeraRoot, Santa Monica, CA, USA) featuring three distinct roughened surface treatments: coated, uncoated, and acid-etched.	Comparative observational	III	831	5 years	-	95% (92.77% for uncoated implants, 93.57% for coated implants, and 97.60% for acid-etched implants)	-	Surface variants pooled; center effects	-	[166]
Dental implant-supported prostheses, including SCs (two-piece implant)	Zirconia implants (ZERAMEX® T, ZrO2-ATZ-Bio-HIP, Spreitenbach, Switzerland)	Prospective	III	76	Up to 3 years	Posterior	87.3% (2-year) 85% (3-year cumulative)	4% (cumulative)	Early gen; aseptic loosening notable	Aseptic loosening (13%), abutment fracture (2.6%)	[127]
Implant-supported fixed complete dentures (Zir-IFCDs)	Zirconia	Retrospective cohort	III	67	5 years	Anterior, Posterior	70.9%	13.4% (cumulative)	Framework fractures in a limited restorative space	Framework fracture (4.4%), all associated with limited vertical restorative space, veneering porcelain fracture (1.5%), implant loss (3.0%), esthetic concerns (3.0%), and one failure of unknown cause (1.5%)	[194]
Implant-supported prostheses, including SCs and 3-unit FDPs	ATZ implants	ProspectCohort	III	53	5 years	Anterior, Posterior	94.3%	8.3% (cumulative)	MBL > 2 mm endpoint	Marginal bone loss > 2	[195]
Dental implant-supported prostheses, including single-tooth replacements	Zirconia	Prospective	III	30	5 years	Anterior, Posterior	93.3%	40% (cumulative)	Small cohort; maintenance factors	peri-implant mucositis (26.7%), peri-implantitis, and implant failure (6.7%)	[196]
Dental implant-supported prostheses, including SCs and 3-unit FDPs—one-piece zirconia implants	Zirconia	Prospective Cohort	III	71	5 years	Anterior, Posterior	98.4%	1.6% (cumulative)	Good survival; details of hygiene protocols NR	Implant failure (0.7 mm), but stable thereafter	[197]
Dental implant-supported prostheses, including SCs— one-piece implant	Y-TZP (zirconia) with a ZiUnite® surface (Nobel Biocare, Zürich, Switzerland).	Prospective Cohort	III	66	5 years	Anterior, Posterior	78.2%	27% (cumulative)	Higher peri-implantitis/MBL; system-specific	Implant failure (21.2%), peri-implantitis (21.2%), marginal bone loss >2 mm (27%), and implant fracture (1.5%).	[198]
Abutments— Implant-supported SCs with zirconia abutments. Implant Type: Standard Platform (SP) vs. Platform Switching (PS)	Zirconia abutments	Retrospective	III	158	Up to 12 years	Anterior	SP (93.8.%) up to 12 years, PS (90%) up to 5 years	10.1% (cumulative)	Platform/MBL differences; soft-tissue endpoints	Abutment fractures (1.9%) loss of retention (frequency not specified) and marginal bone loss, which was more pronounced in standard platform designs compared to platform-switching designs	[199]
Abutments (two-piece)	Zirconia	Retrospective	III	32	6 years	Anterior, Posterior	100%	21.9% (cumulative)	Screw loosening/chips; small cohort	Abutment screw loosening (3.1%), veneering ceramic chipping (6.2%), crown loosening or decementation (9.3%), and occlusal roughness (3.1%)	[200]
Single-tooth implants supporting veneered porcelain crowns, using zirconia abutments	Zirconia abutments with porcelain veneer	Retrospective	III	29	10 years	Anterior, Posterior	97.9%	~41.4% (cumulative)	Mucositis prevalent; veneer chip & screw issues	Peri-implant mucositis (34.5%), veneering porcelain chipping (6.9%), and abutment screw loosening (6.9%)	[178,201]
Implant-supported single crowns with zirconia abutments	Zirconia abutments	MA	I	429	Up to 5 years	Anterior, Posterior	39.4%	-	Heterogeneous definitions; esthetic outcomes favorable vs. Ti/Au	Low marginal bone loss, least soft tissue discoloration (vs Ti & Au)	[202]

Abbreviations: EV, evidence level; SR/MA, systematic review/meta-analysis; RCT, randomized controlled trial; SC, single crown; NR, not reported.

To interpret the clinical data meaningfully, each study in Table 1 was graded using the Oxford Centre for Evidence-Based Medicine (OCEBM) Levels of Evidence (2011), which are widely adopted in dentistry as a design-based hierarchy. In this framework, Level I denotes systematic reviews and meta-analyses (SR/MA) of clinical studies; Level II, randomized controlled trials (including split-mouth and double-blind RCTs); Level III, analytic observational designs such as prospective or retrospective cohorts; Level IV, uncontrolled case series; and Level V, single case reports or expert opinion, representing the lowest level of certainty [203].

Across these evidence tiers, the most consistent and high-certainty signal for zirconia emerges in single crowns, where Level I–II evidence demonstrates survival rates of roughly 95–98% at one to five years with generally low annual complication rates for both tooth- and implant-supported restorations. Systematic reviews and meta-analyses of all-ceramic and monolithic zirconia crowns, together with RCTs and controlled cohort studies, consistently report high survival and modest technical or biological complication profiles, with performance comparable or superior to metal-ceramic benchmarks in many scenarios [107,115,116,117,131,136].

By contrast, outcomes for veneers and multi-unit fixed dental prostheses (FDPs) are more indication-sensitive and rest largely on Level III–V evidence, warranting more cautious interpretation. For zirconia veneers, short- to medium-term clinical studies, including RCTs, split-mouth designs, case series, and retrospective cohorts, report near-perfect survival (≈100% at 1–4 years) with mainly minor esthetic or marginal issues (e.g., marginal discoloration, mild color change, or isolated debonding) [36,102,105,187,188,189]. However, these reports are limited by small sample sizes, short follow-up, heterogeneous veneer thicknesses, and substantial variation in surface-conditioning and bonding protocols (airborne particle abrasion, experimental acid etching, tribochemical coating, or different 10-MDP–containing adhesives) [36,102,105]. Taken together, the available data support the use of zirconia veneers in selected high-masking anterior indications, provided that enamel-preserving preparations, standardized airborne-particle abrasion, and MDP-based bonding protocols are followed—and that patients are clearly informed about the limited long-term evidence [36,102,105,187,188,189].

For single crowns, the evidence base is strong and internally consistent. Systematic reviews and meta-analyses of zirconia-based single crowns, along with prospective clinical cohorts and comparative trials against metal-ceramic crowns, demonstrate survival in the 95–98% range at up to ten years, with most complications being minor or easily manageable (e.g., limited chipping, screw loosening, or small marginal corrections) [107,115,116,117,131,136,200,201]. Prospective cohorts of posterior monolithic zirconia crowns corroborate these findings, reporting excellent 3–5-year survival with relatively low rates of color mismatch, minor surface or marginal adjustments, or isolated debonding and fractures [108,115,116]. This pattern is consistent with the underlying materials science: monolithic 3Y/4Y-stabilized zirconia provides a generous toughness margin for high posterior loads, whereas 4Y/5Y-rich, more translucent formulations are better suited to esthetically demanding anterior sites with lower functional stress [16,20,22,26,27,31,36,38,70,71,72,101,118,119,120,121,122]. Importantly, both In Vitro and In Vivo evidence indicate that polishing, rather than thick glazing, optimizes fatigue resistance and limits antagonist wear. Properly polished zirconia exhibits wear behavior comparable to or even more favorable than conventional dental porcelains when occlusal surfaces are carefully finished [39,40,41,42,79,124,125,126].

Performance in FDPs is clearly design-dependent. Long-term data on veneered 3Y-TZP frameworks show a progressive accumulation of technical complications, especially veneer chipping, connector fatigue, loss of retention, and marginal issues, with survival declining to approximately 63–84% at 10–15 years for multi-unit posterior bridges [112,132,133,135,137,192,193]. In contrast, conservative anterior cantilever resin-bonded FDPs in zirconia demonstrate excellent longevity, with survival around 98% at ten years and relatively low rates of debonding or minor chipping, particularly when used for short spans under favorable load conditions [190,191]. These findings underscore that short span length, favorable load direction, robust connector dimensions, and minimal veneering are key determinants of success. Consequently, current clinical trends favor monolithic or minimally veneered zirconia frameworks with generous connectors for posterior FDPs, reserving extensively veneered posterior zirconia bridges for carefully selected esthetic cases; the supportive data for these indications are still largely Level III [112,132,135,137,190,191,192,193].

In implant-supported restorations and abutments, the architecture of the system strongly influences outcomes. Recent systematic reviews and meta-analyses report approximately 95% 10-year survival for zirconia implants overall, with survival and success figures comparable to titanium when modern systems are considered, though many failures occur early and are associated with specific designs (e.g., narrow diameter, early-generation or discontinued models) [156,160,163,165]. Prospective cohorts of zirconia implants restored with single crowns or short-span FDPs, particularly in two-piece configurations and/or combined with titanium or hybrid abutment concepts, show high five-year survival with stable marginal bone levels and manageable technical complications [127,159,160,195,196,197]. Abutment-level studies indicate that zirconia or zirconia–titanium hybrid abutments can provide favorable soft-tissue esthetics, reduced mucosal discoloration, and good peri-implant tissue health, particularly in the anterior region with thin biotypes, while maintaining acceptable mechanical reliability when Ti-bases or metal inserts are used at the implant–abutment interface [91,96,164,173,174,175,176,177,178,179,186,199,202].

By contrast, certain one-piece zirconia implant systems and narrow-diameter designs demonstrate lower survival (≈78–87% at five years) and higher rates of peri-implantitis, marginal bone loss, or fractures, especially in early-generation or prototype systems [160,166,195,196,197,198]. As a result, for posterior and high-load regions, current evidence favors two-piece or Ti-base hybrid concepts, which better balance mechanical resilience with favorable soft-tissue response, while one-piece zirconia implants and fully ceramic abutments in high-stress molar regions should be selected with caution and placed under stringent maintenance protocols [127,156,160,165,166,167,170,173,174,175,176,177,178,179,186,195,196,197,198,199,200,201,202].

Overall, the highest certainty resides in Level I–II evidence for zirconia single crowns, where long-term survival and complication rates are now well characterized and generally favorable [107,115,116,117,131,136,200,201]. Moderate certainty applies to posterior monolithic crowns and selected implant cohorts employing two-piece or Ti-base hybrid designs [108,115,116,117,127,136,159,160,195,196,197,199,202], while lower certainty characterizes veneers and many FDP configurations, where much of the evidence is Level III–V and highly context-specific [36,102,105,112,132,133,135,137,187,188,189,190,191,192,193]. Interpretation across studies is further complicated by substantial heterogeneity in design, follow-up duration (1–15 years), zirconia generation (veneered 3Y Vs. Monolithic 3Y/4Y/5Y), finishing (Polished Vs. Glazed), and bonding or cementation protocols. Survival and success are defined variably: some authors report annualized rates, others cumulative; minor esthetic corrections or occlusal adjustments are sometimes counted as failures and sometimes not; and several cohorts exclude high-risk groups such as bruxers, potentially inflating apparent success [107,108,112,115,116,117,131,135,137,190,191,192,193].

Clinically, these data support clear, pragmatic guidance. Zirconia veneers should be considered short-term, technique-sensitive solutions for demanding masking in anterior regions, optimally with enamel-preserving preparations, airborne-particle abrasion, and MDP-based bonding [36,102,105,187,188,189]. Monolithic 3Y/4Y zirconia crowns remain the high-certainty choice for posterior load-bearing sites, while more translucent 4Y/5Y variants are best reserved for esthetically critical anterior regions with controlled occlusal forces [16,20,22,26,27,31,36,38,70,71,72,101,115,116,117,118,119,120,121,122]. FDPs are best designed as short-span, monolithic or minimally veneered restorations with robust connectors, limiting extensive veneering in posterior arches wherever possible [112,132,135,137,190,191,192,193]. For implants and abutments, two-piece or Ti-base hybrid zirconia solutions combined with strict maintenance protocols currently represent the most reliable option, especially posteriorly, while one-piece zirconia implants and fully ceramic abutments in high-load regions should be used selectively and monitored carefully [127,156,159,160,165,166,167,173,174,175,176,177,178,179,186,194,195,196,197,198,199,200,201,202]. In summary, zirconia shows high clinical reliability where the evidence is strongest (in single crowns) while outcomes in veneers, FDPs, and implants are more variable and indication-dependent, emphasizing the need for standardized clinical protocols, longer follow-ups, and transparent bias reporting to further strengthen future evidence.

3.6. Challenges and Future Perspective

Despite significant progress, zirconia-based dental ceramics still face several challenges that stop them from achieving their full potential in clinical dentistry. One primary concern is long-term durability. Zirconia is susceptible to low-temperature degradation (LTD or also known as aging) when exposed to moisture and stress over time. Because of that, it can lead to a gradual phase transformation from t→m, suffering microcracking and strength loss [204,205,206,207]. This aging phenomenon can compromise the mechanical properties and longevity of zirconia restorations in the oral environment. To counter this, doping strategies have been employed to mitigate this process. For example, it has been shown that adding stabilizers like CeO₂ or Al₂O₃ or increasing yttria content (from the conventional 3 mol% Y₂O₃ to 4–5 mol%) can reduce the degree of LTD without affecting the material’s grain size or strength. Higher yttria content partially stabilizes more of the cubic phase; therefore, translucency and resistance to degradation are enhanced. However, this approach can compromise mechanical toughness, since transformation toughening is reduced in high-cubic formulations. Some newer 4Y/5Y-ZTP formulations maintain comparable strength to 3Y-ZTP while offering better translucency. Further research is required to fine-tune microstructure and composition for ideal performance [204,208]. Recent developments have also explored co-doping approaches (e.g., adding lanthanum or cerium oxides) to enhance both translucency and aging resistance, though more clinical validation is still needed. In these systems, rare-earth oxides such as La₂O₃ tend to segregate at grain boundaries or form complex phases (e.g., lanthanum aluminate or lanthanum dizirconate), which pin grain growth, reduce oxygen-vacancy mobility, and slow the water-assisted t→m transformation responsible for LTD. This grain-boundary engineering also slightly increases the cubic phase fraction and can reduce refractive-index mismatch between grains and grain boundaries, thereby improving light transmission while maintaining or even improving flexural strength [209]. Ceria co-doping (Y–Ce or Y–Ce–La systems) similarly alters defect chemistry and lattice parameters; low CeO₂ contents can enhance fracture toughness and LTD resistance by stabilizing the tetragonal phase and reducing surface transformation, but higher levels may promote larger grains and secondary phases that impair translucency [210]. Recent work on ternary rare-earth co-stabilized zirconia (e.g., 1.5Y–5.5Ce–0.3La–ZrO₂) confirms that carefully tuned multi-dopant compositions can simultaneously optimize optical properties and hydrothermal stability, suggesting a promising route for next-generation monolithic and implant-grade zirconias [211]. However, most data are still In Vitro (autoclave aging, flexural tests, optical measurements). Long-term clinical trials on these co-doped materials, including their color stability, wear behavior, bonding performance, and failure modes under real oral conditions, are still lacking and represent a key challenge for their routine clinical adoption [101]. Other strategies to reduce aging include inducing compressive surface stresses through polishing (rather than a polished finish) or applying heat treatments to effectively close the tips of the cracks, further stopping crack propagation. Thereby, careful surface engineering is critical in preserving durability, regardless of yttria content [212]. Methods like air-article abrasion, laser irradiation, and using 10-MDP primers have been shown to fortify the bonding interface and enhance structural stability. While they are mainly used to improve adhesion, they may also play a role in disrupting pathways for aging by densifying the surface or filling surface flaws [212,213].

Grain size is another important aspect that influences the aging process. Smaller grains help stabilize the tetragonal phase and resist degradation [214]. Roitero et al. demonstrated that mechanical strength and resistance to degradation were enhanced by nanometric grain sizes at around 110 nm [215]. Also, advanced techniques like flash sintering or adding grain growth inhibitors can regulate grain size distribution to maximize durability. By incorporating nano-zirconia (15 wt%), it was observed that the grain size was significantly suppressed due to its grain boundary pinning effect [216,217]. One major area of innovation, but also of technical limitation, is additive manufacturing (AM) of zirconia. While AM offers mass customization, reduced material waste, and the possibility of highly complex geometries, its broad clinical adoption is still constrained by fundamental materials-science challenges. First, the mechanical reliability of printed zirconia is strongly influenced by flaws introduced during layer-by-layer fabrication, including interlayer porosity, shrinkage-related voids, and defects associated with binder burnout. Fractographic analyses of stereolithography/DLP-printed zirconia consistently show layer interfaces, pores, and debinding defects acting as critical flaw origins, in contrast to the more homogeneous microstructure of milled zirconia [218,219,220]. Systematic comparisons indicate that, although mean flexural strengths of some printed systems can approach those of milled materials, printed zirconia typically exhibits lower Weibull moduli (often in the ~3–10 range), reflecting greater strength variability, whereas milled 3Y-TZP and high-translucency zirconias commonly show m values around 10–20 [48,219,221,222]. This reliability gap underpins the current preference for milled zirconia in high-risk clinical indications.

Second, achieving an optimized, predominantly tetragonal microstructure after sintering is technically demanding in AM workflows. Classic zirconia materials science shows that excessive cubic phase fractions reduce transformation toughening and fracture toughness, while monoclinic contamination and large tetragonal grains compromise aging resistance and long-term strength [222,223]. In AM systems, the combination of high organic content, complex debinding, and orientation-dependent green densities can lead to non-uniform densification, residual porosity, and local variations in grain size and phase composition [17,218,220]. Orientation studies on 3D-printed zirconia demonstrate pronounced anisotropy in flexural strength and microstructure, with failure often initiating along layer interfaces or regions of heterogeneous shrinkage [224]. These defects and microstructural inhomogeneities not only reduce flexural strength but also diminish the effectiveness of stress-induced tetragonal-to-monoclinic transformation toughening, which is critical for long-term survival in high-load posterior regions [17,223,225].

To tackle these barriers, current research focuses on (i) zirconia suspensions with carefully tailored particle-size distributions and high solid loadings to improve packing and minimize sintering shrinkage, (ii) photocurable resin/binder formulations designed for complete decomposition during debinding to limit residual carbon and gas-evolution defects, and (iii) post-sintering densification techniques such as hot isostatic pressing (HIP) to heal internal porosity and delamination [17,218,220]. HIP treatment of material-jetted zirconia lattices has been shown to increase density, reduce internal flaws (verified by X-ray CT), and improve mechanical properties, albeit at the cost of additional processing time and expense [226,227]. Reviews of AM zirconia consistently conclude that, although many printed materials already meet or exceed ISO 6872 requirements for high-strength indications In Vitro, long-term clinical evidence and standardized, defect-minimized workflows are still lacking. Until such workflows are established and clinically validated, many authors recommend cautious use of AM zirconia in high-load posterior regions and view its most secure near-term role in lower-to-moderate load indications and situations where the geometric or functional advantages of AM justify the added complexity [17,206,218,219,228].

Another ongoing challenge is esthetic performance. While zirconia’s color and translucency have improved with the development of newer formulations, achieving a lifelike appearance remains difficult to obtain. Traditional zirconia (3Y-TZP) is relatively opaque, and although newer high-translucency grades have mitigated this problem, offering a better appearance of natural tooth enamel, they can still appear dense or chalky in certain lighting [229]. The color stability of zirconia is another factor to look at, as UV light exposure can induce a reversible change in color, likely due to interactions with oxygen vacancies. Although this UV-induced discoloration is not permanent (heat treatment can reverse it), it underscores the careful consideration of environmental factors on zirconia’s appearance [230,231]. Future research should focus on improving optical properties and stability by developing graded or multilayer zirconia restorations that mimic the natural translucency of teeth. Also, novel sintering methods can help produce finer microstructures that scatter less light, thereby enhancing translucency while maintaining mechanical integrity [232,233,234]. Rare-earth co-doping (e.g., with thulium or erbium) has also been shown to induce fluorescence that closely mimics natural dentin under UV light without degrading strength or phase stability [73].

Surface inertness and bonding represent another impediment to the use of zirconia in dentistry. Zirconia is resistant to conventional acid etching or silanization, which complicates the bonding of resin cements and veneering porcelain due to its chemical stability, relative bioinertness, lack of a glassy phase, and high crystalline content [159,204]. Likewise, when zirconia is used for dental implants, its bioinertness can lead to less osseointegration compared to titanium unless the surface is modified. In this way, surface modification techniques are investigated to enhance the material’s adhesion and bioactivity. Laser surface texturing and plasma spraying or sandblasting with bioactive particles are some of the methods used to increase surface roughness and create chemically active sites and improve resin cement bonding, and promote bone cell attachment in implants. Another promising approach is to apply bioactive coatings (e.g., hydroxyapatite, bioactive glass) to enhance osseointegration and create a favorable biological response at the implant interface. However, the long-term stability of these coatings remains a critical limitation. Repeated mechanical loading and thermally or moisture-induced stresses can gradually weaken the coating–ceramic interface, initiating microcracks or leading to partial delamination. These failures are primarily associated with mismatched thermal expansion coefficients, elastic modulus disparities, and residual stresses created during sintering or thermal cycling. In addition, moisture infiltration, particularly relevant in humid or aqueous service environments, can accelerate interfacial degradation by promoting hydrolysis or stress-corrosion effects at microdefects [235]. To address these issues, recent research has focused on interface engineering strategies. Functionally graded or compositionally transitional interface layers have been shown to reduce abrupt changes in thermal and mechanical properties, thereby smoothing stress gradients and improving interfacial toughness under cyclic loading [236]. Likewise, nanostructured deposition techniques, including sol–gel processing, magnetron sputtering, and atomic layer deposition (ALD), enable the formation of ultra-thin, conformal layers with controlled porosity and defect density. Such nano-architectured coatings can enhance adhesion by improving interfacial wetting, mechanical interlocking, and crack deflection pathways. Although these approaches demonstrate promising performance improvements in laboratory studies, challenges remain in scaling them to complex geometries and validating their long-term durability under clinically or industrially relevant fatigue and environmental conditions [93,237,238].

Additionally, novel zirconia-based composites are explored, where zirconia is coupled with nanoparticles (i.e., alumina, silica, or even antimicrobial agents) to obtain antiplaque resistance or even self-healing capabilities to repair microcracks in situ [204,239,240,241,242].

Manufacturing and processing are also frequently encountered obstacles. which influences the future outlook of zirconia dental materials. At present, most zirconia restorations are fabricated by subtractive manufacturing (milling pre-sintered blanks via CAD/CAM) [225,243]. Milling ensures high precision and density but comes with significant material waste and limitations in geometric complexity. Additive manufacturing (AM) of zirconia, such as 3D printing techniques, has come as an innovative alternative that could allow the fabrication of complex, patient-specific restorations and systems with minimal waste, high precision, and low cost. However, printing high-strength ceramics like zirconia is technically demanding, and current AM zirconia systems are not yet as reliable as traditional methods [17,228,244]. Some of the challenges include the preparation of suitable raw materials, including stable zirconia slurries or powders with the right rheological properties for printing and process control to avoid defects. Printed zirconia often exhibits lower density and strength due to residual porosity or microstructural flaws introduced during layer-by-layer fabrication [244,245]. Surface quality and dimensional accuracy of printed parts are also of concern. For example, shrinkage during sintering of a printed zirconia object can cause distortion and make it challenging to achieve the precise fit required for dental restorations. To bridge the performance gap with milled zirconia, further improvements in printer technology, optimization for resin formulations and binder systems, and refinement of printing parameters are needed [244,246,247]. The focus is oriented on developing techniques that increase the density of printed zirconia to optimize particle size distribution, incorporate binders or additives that aid sintering, and post-printing treatments like cold or hot isostatic pressing. Initial studies have shown that with proper processing, 3D-printed 3Y-TZP can achieve mechanical properties comparable to those of milled zirconia. In the future, multi-material and graded printing may allow a single restoration to be printed with varying translucency or composition across different regions, in the same time, closely replicating the natural tooth structure. Such advancements in manufacturing will enhance customization and could expand zirconia’s use to innovative applications in implants and tissue engineering scaffolds [244,248,249].

Future research directions are oriented toward overcoming the current limitations to improve clinical outcomes. One recommendation is to conduct more mechanical evaluations of zirconia under conditions that simulate the oral environment. For example, to ensure their durability and reliable performance In Vivo, specimens can be subjected to thermal cycling, moisture, and long-term cyclic loading [204]. Long-term studies on humans are also of great importance because they provide data on zirconia’s behavior over the years. They show valuable insights into how it interacts with surrounding tissues and any potential issues that might occur. In terms of material development, next-generation zirconia formulations are expected to significantly enhance clinical performance. This includes nanostructured zirconia (with refined grain sizes for improved translucency and strength) and zirconia hybrids, where zirconia is combined with polymers or glass phases to produce materials that blend the toughness of composites with the hardness of ceramics. Each innovation seeks to achieve the challenging combination of high strength, fracture toughness, excellent esthetics, and bioactivity [204,250]. Balancing these properties remains a difficulty, as increasing translucency can undermine toughness, and enhancing toughness through phase transformations can reduce aging resistance, but innovative material science approaches (e.g., core/shell grain structures, dopant partitioning, or transformation-hardenable glass-infiltrated zirconia) may offer solutions [251,252,253]. Furthermore, functional enhancements are being investigated, like embedding antimicrobial agents (such as silver, gold, or copper nanoparticles) into the zirconia matrix to reduce bacterial colonization on crowns and implants, or engineering zirconia surfaces that can self-heal minor cracks through stress-induced phase transformations or diffusion of healing agents. While many of these ideas are in the experimental stage, they represent promising avenues to extend zirconia’s capabilities [254,255,256].

Zirconia ceramics are now a key part of restorative and implant dentistry. However, in order to achieve their full potential, some problems with stability, optical performance, bonding, and manufacturing reliability still need to be solved. Ongoing improvements in composition and microstructure make materials more resistant to degradation and open up new esthetic possibilities. New ways of making things are also making design more precise and customizable. In the future, progress is likely to move toward integrated, multifunctional strategies. These include defect-controlled additive manufacturing, interface-engineered bioactive coatings, and multi-dopant or nano-architectured grain designs that meet mechanical, optical, and biological needs all at once. Next-generation zirconia systems are ready to offer long-lasting, fatigue-resistant performance without sacrificing esthetics as these new technologies become more reliable through standardized testing and long-term clinical studies. This will further cement zirconia as a cornerstone of modern dental practice.

4. Glass-Based Ceramics

4.1. Composition and Structure

Glass ceramics are polycrystalline solids formed by the controlled crystallization of parent glass. In practice, a precursor glass is heat-treated, a process called “ceramming”, to precipitate one or more crystalline phases within an amorphous matrix [12]. This offers a fine microstructure with dispersed crystals that improve properties while retaining some glassy characteristics. While the general principles of glass–ceramic processing are well-established, recent studies have emphasized modifying the microstructure to optimize strength-translucency trade-offs, which represents a persistent challenge in restorative ceramics. Non-zirconia dental glass–ceramics typically have silica-based glass matrices with varying crystal types grown in situ. For example, leucite (KAlSi₂O₆) and lithium disilicate (Li₂Si₂O₅) are common crystal phases used to strengthen dental porcelains, but modifications to crystal volume, shape, and distribution continue to refine their performance for different clinical indications [257].

Leucite-reinforced feldspathic ceramics (first introduced in the 1990s, e.g., IPS Empress) contain around 35–45% leucite by volume, with crystals of sizes varying from 1 to 5 µm, homogeneously distributed in a silica–alumina glass [256,258]. These leucite crystals precipitate during cooling and impart compressive residual stresses in the glass, increasing strength without significantly reducing translucency (the refractive index of leucite (~1.51) closely matches that of the glass phase). However, despite these improvements, their mechanical performance limits them to anterior and low-stress applications [12].

Lithium disilicate glass–ceramics (commonly Li₂O–Al₂O₃–SiO₂-based) have a higher crystalline content and a different microstructure. The most commonly used glass material is lithium disilicate restorative glass–ceramic, which contains ~70% by volume of interlocking rod-like Li₂Si₂O₅ crystals [12]. These needle-like crystals form an interlocking mesh that reinforces the material. Examples found on the market include the IPS e.max series, introduced in the mid-2000s, which utilizes lithium disilicate and lithium silicate crystals for improved strength and esthetics [259]. The glass composition is tailored with nucleating agents (e.g., P₂O₅, TiO₂) to control crystal formation and size during fabrication. Recent innovations include zirconia-reinforced lithium silicate (ZLS) ceramics, which incorporate nano-scale ZrO₂ particles (~8–10 wt%) into the silicate glass matrix. This nano-phase refinement aims to improve mechanical strength while enhancing translucency by avoiding large-scale light scattering. ZLS ceramics achieve higher strength and translucency because ZrO₂ nanoparticles refine crystal growth (through heterogeneous nucleation and growth inhibition) and remain optically inactive at visible wavelengths. Thus, strengthening the microstructure without compromising esthetics. Materials like Celtra Duo (Dentsply Sirona, Charlotte, NC, USA) and Vita Suprinity (VITA Zahnfabrik, Bad Säckingen, Germany) exemplify this trend and have been positioned as intermediate solutions between traditional lithium disilicate and more opaque zirconia-based ceramics [12,260,261]. The evolution from leucite to lithium disilicate and, more recently, zirconia-reinforced lithium silicate (ZLS) glass–ceramics illustrates the ongoing effort to balance strength and translucency in restorative materials. ZLS represents a shift from compositional adjustment to nanoscale microstructural engineering, where dispersed ZrO₂ refines crystal growth and bridges the gap between glass-based and zirconia-based systems. Most recently, an “advanced lithium disilicate” (ALD) ceramic has been introduced, incorporating an additional lithium aluminosilicate phase (virgilite) within a Li₂Si₂O₅ glass matrix containing some ZrO₂. Upon firing, this ALD (exemplified by Dentsply Sirona’s CEREC Tessera) forms a dual-crystal network that enables extremely rapid crystallization (~4 min furnace cycle) and achieves ~30% higher biaxial strength (reported >700 MPa) compared to conventional lithium disilicate [262,263]. The shift to such multi-phase, nano-crystal engineered glass–ceramics underscores how compositional innovations continue to push the performance of glass-based systems beyond what earlier formulations achieved.

4.2. Mechanical Properties

Glass–ceramics are brittle materials, but their mechanical properties are superior to those of pure glasses due to the reinforcing crystalline phases. The interlocked or dispersed crystals act to hinder crack propagation and can induce beneficial residual stresses. For example, leucite crystals (with a higher thermal expansion coefficient than the glass) create compressive stress in the surrounding matrix upon cooling, while a high volume fraction of rod-like lithium disilicate crystals forms an interlocking network that deflects cracks. Leucite glass–ceramics, for instance, have bending (flexural) strengths on the order of ~140 MPa and fracture toughness ~1.3 MPa·m½ [12,260]. One commercial leucite glass–ceramic reported a flexural strength of ~138 MPa [264]. While this is relatively modest, the inclusion of leucite roughly doubled the strength and toughness compared to a purely glassy porcelain. The strengthening mechanisms include dispersion toughening (crystals deflecting and blunting cracks) and thermal residual stress. Leucite has a higher thermal expansion coefficient than the base glass; as it cools, the crystals put the surrounding glass in compression, which helps counteract tensile stresses from biting forces, thereby improving crack resistance [12,257,265,266].

Lithium disilicate (LD) glass–ceramics are currently among the strongest dental glass–ceramics. With approximately 70 vol% of interlocked Li₂Si₂O₅ crystal needles, they achieve flexural strengths in the range of 350–400 MPa and fracture toughness around 2.3–3.0 MPa·m½. These values are more than twice those of leucite-based ceramics, enabling lithium disilicate restorations to serve in higher-stress applications like posterior crowns. The high crystal content and interlocking morphology effectively inhibit crack growth under load. Additionally, the Vickers hardness of lithium silicate glass–ceramics (typically ~5–6 GPa) is comparable to or slightly higher than that of natural enamel (≈4 GPa). This high hardness means the restorations resist wear well, though care must be taken as overly hard ceramics can abrade opposing teeth if not polished—ideally, the ceramic hardness is tuned close to enamel to minimize antagonist wear [8,267,268].

The mechanical evolution from leucite- to lithium disilicate–based systems reflects a sustained effort to optimize the intrinsic trade-off among strength, fracture resistance, and optical translucency in glass–ceramic materials. Through controlled crystallization, a weak glass can be transformed into a composite-like ceramic capable of withstanding functional loads that pure glass cannot. Despite these advances, non-zirconia glass–ceramics still exhibit lower fracture toughness than transformation-toughened zirconia, leaving them susceptible to brittle failure under excessive stress. To overcome these limitations, recent research has focused on nanostructural refinement. Particularly, the development of nanocrystalline ZrO₂–SiO₂ glass–ceramics that achieve flexural strengths exceeding 1 GPa while maintaining translucency. These breakthroughs mark a transition toward nano-engineered microstructures as the prevailing design strategy for reconciling mechanical performance with esthetic requirements in next-generation dental ceramics [265].

4.3. Optical Properties and Esthetic Performance

One of the main advantages of glass–ceramics in dentistry is their superior optical properties, which allow for highly esthetic restorations. The residual glass phase gives the enamel-like translucency, while the selection and size of the crystalline phase are carefully optimized to limit light scattering. Leucite-based porcelains, for instance, exhibit high translucency because the refractive index of leucite closely matches that of the feldspathic glass matrix, minimizing interfacial scattering and producing enamel-like fluorescence and opalescence. Such materials achieve a natural depth of color and remain preferred for veneers, inlays, onlays, and anterior crowns, where visual integration is critical [8,12,267,268,269].

Lithium disilicate glass–ceramics build upon this foundation by combining optical fidelity with superior mechanical strength. Manufacturers provide lithium disilicate in multiple shades and translucency levels to match various clinical scenarios. For instance, IPS e.max lithium disilicate crowns are available in bleach and standard tooth shades (A–D Vita scale), and in high-translucency (HT), low-translucency (LT), or medium opacity forms [266,270]. Finer or denser crystal distributions increase scattering for opacity, while coarser or fewer crystals enhance light transmission [270]. Trace coloring ions (e.g., vanadium, cerium, and manganese) fine-tune hue and fluorescence, integrating with surrounding dentition seamlessly [11,271].

Clinicians often take advantage of the optical properties by fabricating monolithic restorations (single-phase glass–ceramic without a metal core or opaque sublayer) for maximum translucency, or by layering different glass–ceramics (core and veneer) to balance strength and appearance. Unlike traditional opaque core materials, a lithium disilicate crown can be fully contoured and translucent, yet still strong enough for moderate loads [257,272]. In cases where a substructure is needed (such as a dark stump or metal post to cover), a more opaque glass–ceramic can be used as an inner layer to hide the discoloration [273]. Recently, manufacturers have introduced glass–ceramic blocks with built-in color and translucency gradients that mimic the natural enamel–dentin transition. These multi-layer (gradient) materials exhibit a seamless progression from a more opaque, chromatic cervical/dentin region to a translucent incisal region within the same restoration. As a result, a monolithic glass–ceramic crown or veneer can display natural depth and lifelike incisal translucency without any manual layering, thereby enhancing esthetics and simplifying the fabrication process [274].

4.4. Biocompatibility

Glass–ceramic biomaterials are generally regarded as highly biocompatible and inert. Because of that, they are suitable for the reconstruction and restoration of teeth. They are capable of forming direct bonds with bone and actively promote favorable biological responses at the interface between the material and the surrounding tissues [8]. In the oral environment, silica-based glass–ceramics are chemically stable. They do not corrode or dissolve significantly in saliva. In Vitro assessments have found modern lithium silicate ceramics to be non-cytotoxic and non-genotoxic, meeting stringent biocompatibility standards [275]. So far, there are no documented clinical cases of allergic responses or lasting negative effects associated with lithium silicate ceramics on teeth or surrounding tissues [276,277,278]. Lithium silicate glass–ceramics were classified as biocompatible by NAMSA (North American Science Associates) guidelines for cytotoxicity, genotoxicity, and systemic toxicity [275]. Experimental studies further clarify the cellular mechanisms underlying this biological compatibility. Jung et al. investigated the biological response of human gingival fibroblasts (HGF-1) to lithium silicate-based glass ceramics (LDS) compared to zirconia and titanium with two surface roughness levels (0.07 µm and 0.2 µm). The results showed that LDS supported high levels of fibroblast proliferation. No significant cytotoxic effects and lower LDH release were observed than with zirconia, especially in the early stages of contact. Furthermore, LDS exhibited the lowest inflammatory response, as marked by the expression of TNF-α among all the tested materials. Also, according to the SEM analysis, healthy cell morphology and uniform adhesion on both LDS surface textures were also confirmed [279]. These findings imply that regardless of the roughness levels, fibroblast adhesion and proliferation were promoted by the LDS surfaces. Based on the discoveries of Brunot-Gohin et al., it appears that the surface treatment of lithium disilicate ceramics influences their biocompatibility with soft tissues. In the study, it was observed that the polished surfaces significantly enhanced epithelial cell adhesion and proliferation compared to glazed surfaces. Most importantly, none of the surfaces demonstrated cytotoxic effects on the organotypic epithelial culture model [280]. Further evidence supports the biocompatibility of other glass–ceramics, such as IPS Empress CAD, a leucite-reinforced glass–ceramic. This material presents excellent chemical stability, minimal solubility, and low tendency for plaque accumulation. Cytotoxicity tests have shown that it maintains the cell viability above 80%, with no adverse tissue reaction being observed. Additionally, its long-term compatibility and safety in the oral environment have been confirmed by clinical studies conducted over 10 years [268]. However, the current trend in material science extends beyond passive biotolerance toward functional bioactivity. New formulations, like nano-engineered ZrO₂–SiO₂ and ion-releasing glass–ceramics, try to combine the stability of traditional systems with controlled ion exchange and protein adsorption features that help seal soft tissue and promote osteogenic potential [281,282,283]. In this context, the development of glass–ceramics shows a progression from “biocompatible and inert” to “biointeractive and regenerative”. This new generation of materials intends not only to coexist with biological tissues but to actively participate in healing and integration processes, making a breakthrough in the design of restorative ceramics.

Figure 2 presents the interplay between composition, structure, mechanical properties, optical/esthetic performance, and biocompatibility in glass-based ceramics for dental applications.

4.5. Clinical Applications of Glass-Based Ceramics

4.5.1. Veneers

Glass dental ceramics, especially lithium disilicate and leucite-reinforced porcelains, have long been represented as a choice for veneers and other conservative restorations due to their great translucency and strong bondability. In contrast to zirconia, silica-based glass ceramics can be etched with hydrofluoric acid to create a long-lasting chemical bond with tooth structure and resin cements. This adhesive bonding permits ultra-thin restorations with minimal or no tooth preparation. For example, lithium disilicate (e.g., IPS e.max) veneers as thin as ~0.3–0.5 mm have been successfully used in no-prep or minimal-prep cases [284,285]. Sulaiman et al. evaluated 2988 lithium disilicate (IPS e.max) veneers over 45 months. This included 1612 monolithic veneers, of which 21 failed, resulting in a fracture rate of 1.3%. Additionally, 1376 layered veneers were evaluated, and they also had 21 failures with a slightly higher rate of fractures of 1.53%. These low failure rates confirm the excellent short-term clinical performance of both monolithic and layered lithium disilicate veneers [284].

The longevity and clinical success of laminate veneers rely on a minimum, primarily enamel-based preparation, as well as a strong adhesive bond between the ceramic-tooth interface. This represents a key advantage over zirconia veneers (which are inherently more challenging to bond). Feldspathic porcelain and leucite-reinforced glass ceramics are highly valued for their superior esthetic properties, particularly due to their ability to closely replicate the natural shade and translucency of tooth enamel. However, their relatively low mechanical strength limits their durability. Lithium disilicate ceramics provide an optimal balance between esthetics and mechanical performance, having an improved structural resilience than feldspathic and leucite-reinforced ceramics [285]. Recent meta-analysis data reinforce the long-term clinical effectiveness of glass ceramic veneers for anterior and premolar restorations. Lithium disilicate veneers demonstrated the highest survival rate over a mean period of 10.4 years (96.81%) among glass ceramics, outperforming feldspathic (96.13%) and leucite-reinforced ceramics (93.70%) [286]. Furthermore, the lithium disilicate veneers showed the lowest long-term rate of technical (6.1%), esthetic (1.9%), and biological (0.45%) complications, suggesting a favorable combination of strength, longevity, and esthetic performance. These findings indicated that lithium disilicate veneers were the best option for long-term veneer applications in the anterior and premolar areas [287].

In clinical applications, lithium disilicate veneers have been praised for their enamel-like translucency and, being able to blend seamlessly with adjacent teeth. In contrast, traditional 3Y-TZP zirconia is too opaque for such indications. Even with newer translucent zirconia formulations, glass–ceramics continue to perform better in mimicking natural tooth enamel (approximately 30% greater translucency than conventional zirconia ceramics of similar thickness). However, this high translucency also means that underlying discoloration may affect the final appearance. In cases where a dark substrate needs to be masked, clinicians may opt for more opaque ceramics. Manufacturers offer lithium disilicate ingots in various opacity levels. For instance, High Opacity (HO) ingots to mask dark dentin or metal cores, versus High Translucency (HT) or Enamel ingots for maximum esthetics [70,288,289,290,291].

A significant advantage of glass–ceramic veneers is that their brittleness is mitigated by bonding. Although lithium disilicate’s flexural strength (330–400 MPa) is lower than zirconia’s (900–1200 MPa), once the restoration is adhesively bonded to the tooth structure, it can distribute stresses effectively. In fact, it has been demonstrated that a thin (0.3 mm) lithium disilicate veneer bonded with resin can have higher or comparable fracture resistance than 0.6 mm veneers, thanks to the reinforcing effect of the underlying tooth structure [292,293]. Clinically, glass–ceramic veneers demonstrate remarkable durability. A large retrospective study of 1075 CAD/CAM lithium disilicate veneers with feather-edge margins reported a cumulative survival rate of 99.83% over a mean period of 30.8 months, with minimal fractures and exceptional esthetic outcomes [294]. Glass–ceramics exhibit low wear against opposing teeth when properly polished. Their hardness (approximately 6 GPa Vickers) is close to natural enamel and far less abrasive than poorly glazed ceramics. Accordingly, long-term studies have found that enamel wear from lithium disilicate restorations is negligible and comparable to that of enamel-enamel contact [277,278,285,286]. In conclusion, glass–ceramics prove to be a very successful material, which provides a balance between mechanical performance and eeesthetics. Their strong adhesive bonding compensated for their brittleness, and their enamel-like translucency facilitates their seamless integration. Long-term clinical evidence supports their excellent durability, minimal wear on opposing dentition, and high survival rate even in ultra-thin application, making them a reliable and esthetically superior choice for various restorative applications.

4.5.2. Inlays, Onlays

Glass ceramics have become the materials of choice for inlays and onlays due to their excellent bonding capability and favorable esthetic and mechanical properties [284]. A retrospective clinical study focusing on pressed lithium disilicate inlays and onlays in posterior teeth found them to be clinically reliable over a period up to 8.3 years. Among all the 143 restorations that were evaluated, the cumulative survival rate was 97.5% after almost 6 years and 95% after 8.3 years. All failures (3.5%) occurred in onlays, while no inlay failures were recorded during the study period. The restorations were adhesively bonded using a total-etch technique and maintained functional and esthetic integrity under posterior load. Even when they were placed by dental students, they proved excellent outcomes, highlighting the durability and effectiveness of lithium disilicate for minimally invasive inlay and onlay restorations in posterior regions [295]. Another large clinical prospective study evaluated the long-term performance (14 years) of pressed lithium disilicate restorations in patients with severe occlusal wear. All 14 inlays placed in posterior areas had a 100% survival rate with no recorded failures, while the 97 onlays (placed in similar posterior regions) showed a slightly lower survival rate of 85.7% after 12 years, with only two failures (which occurred in the first 5 years). Importantly, no failures occurred after eight years, indicating that fatigue fracture was not a progressive issue. These findings confirm that lithium disilicate inlays and onlays present long-term durability in load-bearing posterior sites, even in patients with bruxism and heavy occlusion [296]. Similarly, the long-term durability of lithium disilicate inlays and onlays was further confirmed. They presented survival rates of 93.9% and 98.3%, respectively, after 10 years [297]. Additionally, a 16.9-year retrospective study conducted by Malament et al. evaluated 314 partial coverage lithium disilicate restorations (including inlays and onlays) and reported a 95.27% survival rate. It was concluded that restoration thickness, tooth position, and patient-related variables had no significant impact on longevity, reinforcing the material’s robustness in high-stress posterior applications [298]. These excellent clinical outcomes are closely linked to the materials’ ability to adhesively bond to tooth structure, which permits conservative preparations. Only diseased or damaged tooth structure needs to be removed, preserving as much healthy enamel as possible for bonding. The strong resin–ceramic bond provides retention and reinforces the restoration-tooth complex, even allowing thin restorations in some cases. In contrast, zirconia onlays (while very strong intrinsically) cannot be acid-etched and bonded as reliably, so they generally require more aggressive preparation or mechanical retention. Lithium disilicate inlays and onlays can often be placed with minimal reduction and still achieve excellent stability thanks to adhesive luting. Notably, their high fracture resistance allows for obtaining reduced thickness, such as onlays as thin as ~1.0–1.5 mm, which have shown success even under heavy occlusal loads. This makes them suitable for patients with bruxism or high bite forces, provided that a minimum ceramic thickness (around 1 mm) is ensured on functional cusps [299,300,301,302,303]. In conclusion, lithium disilicate glass ceramics are well-suited for inlays and onlays, including in posterior regions subjected to high occlusal forces.

4.5.3. Crowns and Short-Span Bridges

Lithium disilicate glass–ceramic has become a versatile option for full crowns and small fixed partial dentures (FPDs) in cases where full-zirconia might be unnecessary or where superior translucency is desired. The material offers a balance of moderate strength and high esthetics that suits single-unit crowns in any region, and 3-unit bridges in low-to-moderate stress areas. Modern lithium disilicate is about 2–3 times stronger than earlier leucite or feldspathic ceramics due to its 70% crystalline microstructure. While this is still only roughly half the strength of 3Y-TZP zirconia, it has been shown to exhibit greater resilience to fatigue under cyclic loading compared to zirconia [1,13,271,284]. Long-term studies present excellent outcomes with monolithic lithium disilicate crowns in both anterior and posterior positions. For instance, a 10-year clinical study of nearly 2000 pressed lithium disilicate crowns reported a cumulative 99.6% survival rate, with an extremely low annual failure risk (0.14%). Failures primarily occurred in molar teeth (5/7), affecting both arches. However, no failures were recorded among the 550 bilayer restorations over [304]. A systematic review based on 12 clinical studies that included 696 lithium disilicate single crowns further confirms their reliability for both anterior and posterior use, especially in the short term (1–5 years). Their 3-year cumulative survival rate was 100%, at 5 years it was 97.8%, and at 10 years it was 96.7%. The reported failures were rare (only 9 in total), and they predominantly occurred in the posterior region, where occlusal forces are higher. These failures were generally minor, involving core fractures or chipping of the veneering porcelain. The majority of the restorations were either monolithic lithium disilicate (e.g., IPS e.max Press or CAD, Ivoclar Vivadent, Schaan, Liechtenstein) or bilayered, such as the earlier-generation IPS Empress 2 (Ivoclar Vivadent, Schaan, Liechtenstein) [103]. Given these findings, lithium disilicate crowns offer good performance in both monolithic and bilayered forms in anterior and posterior areas, with few failures reported, mostly of which are minor. Leucite-reinforced glass–ceramics are one of the first generations of esthetic all-ceramic materials, which have been representing for a long time a great choice for single crowns, especially for patients who value translucency and a natural-looking tooth. These materials have an improved fracture resistance compared to conventional feldspathic porcelains, as they can incorporate 40–50% leucite crystals in a glass matrix through mechanisms like crack deflection and thermal mismatch-induced toughening. Although they have a lower flexural strength (143–164 MPa) than lithium disilicate (300–400 MPa), there is evidence that adhesive bonding significantly enhances their load-bearing capacity. Their durability is supported by long-term clinical data in anterior (incisors, canines) and posterior (premolars, molars) placements. A retrospective clinical study of 93 crowns revealed a survival rate of 79.6% over 13–15 years, with the majority of failures (fractures and chipping in 5.4% cases and periodontitis in 4.3% cases) occurring after 11 years. These results affirm that leucite-reinforced glass–ceramics remain a viable choice for anterior and selected posterior single crowns when proper case selection and bonding techniques are followed [305].

Lithium disilicate fracture toughness is 2–3 times higher than that of conventional feldspathic porcelain and leucite-reinforced glass–ceramics but notably less than zirconia [306]. Thus, lithium disilicate crowns are engineered with slightly more bulk (e.g., 1.5–2 mm occlusal thickness) to ensure longevity, especially in load-bearing areas. Tooth preparation guidelines for lithium disilicate crowns typically recommend approximately 1–1.5 mm axial and 1.5–2 mm occlusal reduction for optimal strength and esthetics. In situations of limited occlusal clearance, evidence supports that monolithic lithium disilicate crowns can perform reliably with a reduced occlusal thickness of approximately 1.0 mm without compromising clinical outcomes [288,307]. This was demonstrated in a study conducted by Špehar et al., who compared monolithic lithium disilicate crowns (prepared with 1.0 mm occlusal and 0.6 mm axial reduction) to conventional veneered lithium disilicate crowns (prepared with 2.0 mm occlusal and 1.0 mm axial reduction). After 1 year, the monolithic group showed a 95.5% survival rate, while the veneered group showed a 100% survival rate. Compared to high-strength zirconia that might require less reduction, lithium disilicate still allows more conservative preparation than traditional metal-ceramic crowns. Despite needing less tooth reduction, the monolithic crowns showed no statistically significant differences in performance or patient satisfaction (which was 100% in both groups) [271].

Esthetically, glass–ceramic crowns are often considered the gold standard for realistic appearance. The material can be fully anatomically contoured and then stained and glazed, or a cut-back technique can be used where a monolithic lithium disilicate core is layered with a fine enamel porcelain on the labial/incisal for ultimate translucency. Even in monolithic form, lithium disilicate’s optical properties (refractive index match between crystals and glass, small crystal size ~3–6 µm) impart a translucency and depth that mimics natural dentin and enamel better than most zirconias [12,60,275,308]. Clinical studies confirmed lithium disilicate crowns had significantly better shade match and translucency than zirconia crowns in the anterior region, making them ideal for patients with high esthetic demands. The flip side is that a glass–ceramic crown will not mask underlying dark metal cores or heavily stained teeth as effectively as an opaque zirconia core would. Therefore, case selection is important. In an implant restoration with a titanium abutment, for example, a common approach is to use a zirconia abutment or coping and veneer it with lithium disilicate or porcelain to combine strength with esthetics [272,288,308].

Short-span bridges (FPDs) can be fabricated from lithium disilicate under certain conditions. The typical indication is a 3-unit bridge replacing a single missing tooth, limited to the anterior or premolar region. Manufacturers of IPS e.max specify that bridges involving molar sites are not recommended unless the pontic is a premolar and the terminal abutment is a second premolar. The reason for this limitation is the higher stress and flexure in longer spans and glass–ceramics lack the transformation toughening of zirconia and could develop cracks over time under heavy occlusal loads [309,310]. Nonetheless, within their indicated use, lithium disilicate 3-unit FPDs have shown good mid and long-term performance. Wolfart et al. evaluated 33 lithium disilicate (IPS e.max Press) FPDs over 8 years and observed that they achieved a 93% survival rate. Most complications involved minor fractures in the connector area of the posterior FDPs, underscoring again the importance of adequate connector dimensions and proper stress management [311]. Similarly, Homa et al. investigated 32 CAD/CAM-fabricated lithium disilicate (IPS e.max CAD) FDPs placed in anterior and premolar regions. An 84.4% survival rate and a 75% success rate were reported after 10 years [312]. Other reports found that FPDs have a 5-year survival rate of 95–100%, while a 10-year survival rate ranges from about 71 to 100%, with the lower rates mostly seen in long-span or multi-unit bridges, especially those placed in the posterior region or designed with two retainers. In contrast, three-unit bridges that are placed in the anterior pr premolar regions demonstrated more consistent long-term success [103,313,314]. Overall, zirconia-based ceramics are preferred for long-span or high-load bridges due to their superior strength and fracture resistance. Lithium disilicate, on the other hand, is a strong option for short-span restorations in the anterior or premolar region, especially when superior esthetics or adhesive bonding is desired. For patients who cannot tolerate metal and are missing a premolar or anterior tooth, a lithium disilicate bridge can represent a great metal-free, esthetic solution. However, patients should be informed about the slightly elevated long-term risk of fracture with lithium disilicate compared to zirconia or metal-based frameworks, particularly in posterior applications.

Table 2 presents an overview of the main clinical uses of glass-based materials, including the type and number of restorations tested, evidence level, follow-up duration, anatomical location, survival and complication rates, and the nature of complications encountered, as well as study limitations.

Table 2. A summarization of glass-based materials’ clinical applications.

Type of Restoration	Material	Study Type	EV	No. of Samples Tested	Follow-Up Duration	Tested Location	Survival Rate	Complication Rate (Annual/Cumulative)	Study Limitations	Type of Complications	Ref
Veneers	Leucite-reinforced (LR)	SR/MA	I	125	10.4 years	Anterior, Posterior	93.70%	Technical (29.87%), esthetic (17.89%), and biological (4.4%) (cumulative)	Pooled across studies with variable protocols and outcome criteria, several reports include minor esthetic/technical events as “complications”.	Chipping (0.99%), bulk fractures (7.92%), marginal gaps (41.67%), debonding (8.91%), marginal discoloration (17.89%), secondary caries (1.98%), endodontic complications (1.98%), and tooth loss (0.99%)	[286]
Veneers	Lithium Disilicate (LD)	SR/MA	I	1135	10.4 years	Anterior, Posterior	96.81%	Technical (6.1%), esthetic (1.9%), and biological (0.45%) (cumulative)	Pooled cohorts with differences in adhesive workflows and follow-up schedules; endpoint definitions heterogeneous across studies.	Chipping (0.84%), bulk fractures (0.55%), marginal gaps (12.83%), debonding (2.23%), marginal discoloration (1.9%), secondary caries (0.45%), and endodontic complications (0.84%)	[286]
Veneers	Feldspathic ceramic	SR/MA	I	428	10.4 years	Anterior, Posterior	96.13%	Technical (41.48%), esthetic (19.64%), and biological (6.51%) (cumulative)	Methodological heterogeneity across included studies; minor events variably classified as failures limiting comparability.	Cracks (6.31%), chipping (7.21%), bulk fractures (8.33%), marginal gaps (32%), debonding (5.95%), marginal discoloration (19.64%), tooth fracture (1.19%), secondary caries (2.83%), and endodontic complications (1.80%)	[286]
Veneers	LD	Controlled Clinical Trial	II	36	3 years	Anterior	100%	Technical (37.5%), and biological (43.75%) (cumulative)	Controlled trial; randomization not specified; small sample and short follow-up limit generalizability.	Surface staining (37.5%) and initial hypersensitivity (43.75%), which were mild and reversible	[288]
Veneers	Heat-pressed LR Glass ceramic (Cergo)	Retrospective	III	101	10 years	Anterior	91.8%	23.8% (cumulative)	Single-center retrospective design; operator and bonding/finishing protocols may vary; selection/recall bias possible.	Ceramic fractures (7.9%), recementation (8.9%), minor ceramic chipping managed with polishing (1%), endodontic treatment (2%), and secondary caries requiring composite repair (2%).	[315]
Veneers	Feldspathic porcelain (IPS InLine)	Retrospective	III	78	~3.6 years	Anterior	97.4%	9% (cumulative)	Short-to-mid-term data from practice setting; substrate and cement protocol not standardized.	Catastrophic fractures (2.6%), minor ceramic fractures or cracks (3.8%), marginal discoloration (2.6%), marginal integrity issues (6.4%), and marginal excess material (2.6%)	[316]
Porcelain laminate veneers	Lithium disilicate-reinforced glass–ceramic (IPS e.max Press)	Retrospective	III	358	10 years	Anterior, Posterior	≥99.7%	~2.5% (cumulative)	Retrospective design; possible selection and recall bias;	Small cracks (0.03%), large cracks (0.08%), extensive fractures (0.03%), veneer loss (0.08%), rebonding (0.13%), and secondary caries (0.08%)	[317]
Laminate veneers	Pressable lithium disilicate glass–ceramic (LDLVs)	Retrospective	III	364	10 years	-	97.4%	1.64% (cumulative)	Bonding uniformity not reported in detail.	Fractures (0.55%) and debonding (1.09%)	[318]
Veneers	Feldspathic ceramic	Retrospective	III	170	7 years	Anterior	91.77%	8.23% (cumulative)	Retrospective single-material study; substrate reporting limited; failures often retreated with LD (affecting long-term estimate).	Core fractures (8.23%), all replaced with LD, and surface chipping (5.88%)	[319]
Onlays	Pressed LD glass–ceramic (IPS e.max)	Clinical Study	III	305	>9.8 years	Anterior, Posterior	98.3%	0.29% (cumulative)	Single-material cohort with standardized finishing; good external validity but inter-operator details are limited.	Bulk fracture or large chips, exclusively in molar teeth	[297]
Onlays	Ceramic reinforced with lithium disilicate, conventional feldspathic ceramic, or reinforced with leucite	SR/MA	I	14–231	24–180 months	Posterior	~94.2%	~10% (cumulative)	Mixed materials and protocols pooled; follow-up and endpoint criteria heterogeneous.	Fractures (4%), marginal integrity loss (2.32%), anatomical degradation (2.17%), secondary caries (1.22%), discoloration or color instability (~1%), surface texture degradation (~1–2%), and critical failures requiring replacement (~0.79%)	[320]
Inalys, Onlays	LR	Retrospective	III	132 (107 Inlays; 25 onlays)	11.2 years	Posterior	80.3%	Technical (16.7%), biological (4.5%) (cumulative)	Posterior load retrospective design; material limitations may affect long-term margins; parafunction control not reported.	Ceramic fractures (10.6%) and chipping (2.3%) were the most frequent complications	[321]
Inlays, Onlays	Feldspathic porcelain and other glass-based ceramics	SR/MA	I	3266 restorations (Glass ceramics: 2218 + Feldspathic: 1048) - 10-year follow-up: 2904 restorations (Glass ceramics: 1075 + Feldspathic: 1829)	Up to 10 years	Posterior	- 5-year follow-up: (Glass ceramics: 92% Feldspathic: 90%)- 10-year follow-up: (Glass ceramics: 89% + Feldspathic: 91%)	~3–9% (cumulative)	Pooled protocols and outcomes; survival evaluated at 5 and 10 years with variable criteria.	Fractures (6.2%), endodontic problems (3%), secondary caries (1.7%), and debonding (0.9%)	[322]
Inlays, Onlays	Feldspathic porcelain, LR, LD	Prospective	III	5791 (4475—feldspathic porcelain, 1076—LR glass–ceramic, and 240—LD)	Up to 15 years (Mean: 3 years)	Posterior	~84%	~3.8% (cumulative)	Multimaterial practice-based dataset; operator and indication variability limit comparability.	Ceramic or tooth fractures (44.5%), endodontic complications (16.4%), secondary caries (8.2%), postoperative sensitivity (3.2%), and periodontal complications (2.7%)	[323]
Inlays, Onlays, Overlays	LR and LD	SR/MA	I	605	10 years	Posterior	93%	9% (cumulative)	Mixed ceramics; adhesion and finishing details variably reported; mostly minor repairs.	Fractures/chipping (4%), followed by endodontic complications (3%), secondary caries (1%), and debonding (1%)	[324]
Inlays, Onlays, Crowns	Pressed LD (IPS e.max Press)	Clinical Study	III	2392 (1782— Crowns; 610—Inlays, Onlays)	16.9 years	Posterior	96.49%	0.92% (cumulative)	Practice-based network study; high external validity but protocol adherence varied across centers.	Bulk fracture or large chip	[298]
Inlays	Pressed LD glass–ceramic (IPS e.max)	Clinical Study	III	246	> 9.9 years	Posterior	93.9%	1.22% (cumulative)	Posterior molar-only cohort; occlusal schemes and parafunction not detailed.	Bulk fracture or large chips, all in posterior molars	[297]
Inlays	LD	Retrospective	III	29	8.3 years	Posterior	100%	0%	Small retrospective series; selection bias possible; cement protocol not fully specified.	-	[295]
Inlay, Partial Crown, Crown	LD (IPS e.max Press)	Retrospective	III	250 (inlay— 66; partial crown—174; crown—5)	8.5 years	Posterior	94%	83.8% (cumulative)	Undergraduate clinic data; technique variability across operators.	Fracture (2%), Debonding (0.4%), Endodontic (0.8%), Caries (0.8%)	[325]
Partial crowns	LD	Retrospective	III	114	8.3 years	Posterior	95%	Technical (2.7%), esthetic (1.8%), and biological (5.3%) (cumulative)	Mixed substrates and preparation designs; maintenance protocols not reported.	Debonding (0.9%), marginal staining (1.8%), secondary caries (2.6%), irreversible pulpitis (1.8%), and tooth loss (0.9%)	[295]
Crowns	IPS Empress 2	Prospective	III	27	5 years	Posterior	100%	0%	Small prospective cohort; posterior-only; limited statistical power.	None observed	[326]
Crowns	LD (IPS e.max Press, IPS e.max CAD, IPS Empress 2)	SR	I	696	Up to 10 years	Posterior, Anterior	100% at 2 years, 97.8% at 5 years, and 96.7% at 10 years	~1.3% (cumulative)	Pooled crown cohorts; monolithic/veneered distinction inconsistently reported; endpoint criteria variable	Core ceramic fractures (~0.7%) and veneering chipping (~0.6%), mostly occurring in the posterior region, while endodontic issues, secondary caries, and debonding	[103]
Crowns	LD (IPS e.max)	Clinical Study	III	22 (conventional veneered crowns), 22 (reduced-thickness monolithic crowns)	1 year	Posterior	100% veneered crowns, 95.5% monolithic crowns	0% veneered crowns, 4.5% monolithic crowns (cumulative)	Short-term comparison; small sample; limited inference for long-term posterior use.	Catastrophic fracture (occlusal surface, required replacement)	[271]
Monolithic and Bilayered Crowns	LD (IPS e.max)	Clinical Study	III	1960	Up to 10.4 years	Anterior, Posterior	Monolithic: 96.5% at 10.4 years Bilayered: 100% at 7.9 years	Monolithic: 0.21% Bilayered: 0% (annually)	Mixed clinical settings; tooth-type and load stratification partial; good external validity	Fracture (bulk or large chip requiring replacement), Minor chips noted but did not require replacement unless significant	[304]
Crowns	LR	Clinical Study	III	93	Up to 15 years	Anterior, Posterior	79.6%	20.4% (cumulative)	Older-generation material; very long follow-up; higher event rate reflects material and indication era.	Fractures/chipping (5.4%), periodontitis (4.3%), occlusal wear	[305]
Crowns	LD	SR	I	~1500+	Up to 15 years	Anterior, Posterior	87.1–100%	<1%–16.6% (cumulative)	Pooled across indications and designs; heterogeneous reporting of success vs. survival.	Fractures of the crown or core (~1–3%), veneer chipping in bilayered restorations (2–5%), loss of retention (1–4%), need for endodontic treatment (2–3%), gingival inflammation (~2–5%), marginal caries (<1–2%), and debonding or dislodgement (~1–3%).	[313]
Bridges (3-unit)	IPS Empress 2	Prospective	III	31	5 years	Anterior, Posterior	70%	19.4% (cumulative)	Early-generation framework; connector stress and span length limit longevity.	Framework fractures (9.7%), biological failures (6.5%), and an irreparable partial veneer fracture (3.2%).	[326]
Bridges	LD (Mainly IPS e.max Press, IPS Empress 2)	SR	I	145	Up to 10 years	Posterior	83.3% at 2 years, 78.1% at 5 years, and 70.9% at 10 years	17.2% (cumulative)	Posterior spans pooled; connector and load variability across studies.	Core/framework fractures, veneering ceramic chipping, debonding, endodontic issues, and secondary caries	[103]
Bridges (3-unit)	LD (IPS e.max Press)	Clinical Study	III	33	Up to 8 years	Anterior, Posterior	93%	6% (cumulative)	Small single-material cohort; connector dimensions and indication limit generalizability.	Fractures requiring replacement (6%), chipping of the veneering ceramic (6%), loss of retention requiring recementation (6%), and endodontic complications in abutment teeth (3%)	[311]
Bridges (3-unit)	Monolithic CAD/CAM LD	Multicenter	III	32	10 years	Anterior, Posterior	84.4%	15.6% (cumulative)	Multicenter design; endpoint heterogeneity and maintenance protocols vary across sites.	Connector fracture (3.1%), repeated debonding (3.1%), persistent pain (6.2%), abutment loss (3.1%)	[312]
Bridges (3-unit)	LD	SR	I	~270+	Up to 15 years	Anterior, Posterior	48.6–100%	2.7–46% (cumulative)	Wide indication mix; high heterogeneity	Fractures at the connector or pontic area (3–10%), loss of retention or debonding (4–6%), persistent or post-operative pain (2–5%), endodontic complications in abutment teeth (2–3%), chipping of veneering ceramic (2–6%), and biological complications such as periodontal issues or marginal inflammation (~2–4%)	[313]
Bridges	LD (IPS e.max, Empress)	Integrative Review	I	35	Up to 6 years	Anterior	100%	0%	Small sample	None observed	[314]

Abbreviations: EV, evidence level; SR/MA, systematic review/meta-analysis; LD, lithium disilicate; LR, leucite-reinforced; NR, not reported.

Table 2. A summarization of glass-based materials’ clinical applications.

Type of Restoration	Material	Study Type	EV	No. of Samples Tested	Follow-Up Duration	Tested Location	Survival Rate	Complication Rate (Annual/Cumulative)	Study Limitations	Type of Complications	Ref
Veneers	Leucite-reinforced (LR)	SR/MA	I	125	10.4 years	Anterior, Posterior	93.70%	Technical (29.87%), esthetic (17.89%), and biological (4.4%) (cumulative)	Pooled across studies with variable protocols and outcome criteria, several reports include minor esthetic/technical events as “complications”.	Chipping (0.99%), bulk fractures (7.92%), marginal gaps (41.67%), debonding (8.91%), marginal discoloration (17.89%), secondary caries (1.98%), endodontic complications (1.98%), and tooth loss (0.99%)	[286]
Veneers	Lithium Disilicate (LD)	SR/MA	I	1135	10.4 years	Anterior, Posterior	96.81%	Technical (6.1%), esthetic (1.9%), and biological (0.45%) (cumulative)	Pooled cohorts with differences in adhesive workflows and follow-up schedules; endpoint definitions heterogeneous across studies.	Chipping (0.84%), bulk fractures (0.55%), marginal gaps (12.83%), debonding (2.23%), marginal discoloration (1.9%), secondary caries (0.45%), and endodontic complications (0.84%)	[286]
Veneers	Feldspathic ceramic	SR/MA	I	428	10.4 years	Anterior, Posterior	96.13%	Technical (41.48%), esthetic (19.64%), and biological (6.51%) (cumulative)	Methodological heterogeneity across included studies; minor events variably classified as failures limiting comparability.	Cracks (6.31%), chipping (7.21%), bulk fractures (8.33%), marginal gaps (32%), debonding (5.95%), marginal discoloration (19.64%), tooth fracture (1.19%), secondary caries (2.83%), and endodontic complications (1.80%)	[286]
Veneers	LD	Controlled Clinical Trial	II	36	3 years	Anterior	100%	Technical (37.5%), and biological (43.75%) (cumulative)	Controlled trial; randomization not specified; small sample and short follow-up limit generalizability.	Surface staining (37.5%) and initial hypersensitivity (43.75%), which were mild and reversible	[288]
Veneers	Heat-pressed LR Glass ceramic (Cergo)	Retrospective	III	101	10 years	Anterior	91.8%	23.8% (cumulative)	Single-center retrospective design; operator and bonding/finishing protocols may vary; selection/recall bias possible.	Ceramic fractures (7.9%), recementation (8.9%), minor ceramic chipping managed with polishing (1%), endodontic treatment (2%), and secondary caries requiring composite repair (2%).	[315]
Veneers	Feldspathic porcelain (IPS InLine)	Retrospective	III	78	~3.6 years	Anterior	97.4%	9% (cumulative)	Short-to-mid-term data from practice setting; substrate and cement protocol not standardized.	Catastrophic fractures (2.6%), minor ceramic fractures or cracks (3.8%), marginal discoloration (2.6%), marginal integrity issues (6.4%), and marginal excess material (2.6%)	[316]
Porcelain laminate veneers	Lithium disilicate-reinforced glass–ceramic (IPS e.max Press)	Retrospective	III	358	10 years	Anterior, Posterior	≥99.7%	~2.5% (cumulative)	Retrospective design; possible selection and recall bias;	Small cracks (0.03%), large cracks (0.08%), extensive fractures (0.03%), veneer loss (0.08%), rebonding (0.13%), and secondary caries (0.08%)	[317]
Laminate veneers	Pressable lithium disilicate glass–ceramic (LDLVs)	Retrospective	III	364	10 years	-	97.4%	1.64% (cumulative)	Bonding uniformity not reported in detail.	Fractures (0.55%) and debonding (1.09%)	[318]
Veneers	Feldspathic ceramic	Retrospective	III	170	7 years	Anterior	91.77%	8.23% (cumulative)	Retrospective single-material study; substrate reporting limited; failures often retreated with LD (affecting long-term estimate).	Core fractures (8.23%), all replaced with LD, and surface chipping (5.88%)	[319]
Onlays	Pressed LD glass–ceramic (IPS e.max)	Clinical Study	III	305	>9.8 years	Anterior, Posterior	98.3%	0.29% (cumulative)	Single-material cohort with standardized finishing; good external validity but inter-operator details are limited.	Bulk fracture or large chips, exclusively in molar teeth	[297]
Onlays	Ceramic reinforced with lithium disilicate, conventional feldspathic ceramic, or reinforced with leucite	SR/MA	I	14–231	24–180 months	Posterior	~94.2%	~10% (cumulative)	Mixed materials and protocols pooled; follow-up and endpoint criteria heterogeneous.	Fractures (4%), marginal integrity loss (2.32%), anatomical degradation (2.17%), secondary caries (1.22%), discoloration or color instability (~1%), surface texture degradation (~1–2%), and critical failures requiring replacement (~0.79%)	[320]
Inalys, Onlays	LR	Retrospective	III	132 (107 Inlays; 25 onlays)	11.2 years	Posterior	80.3%	Technical (16.7%), biological (4.5%) (cumulative)	Posterior load retrospective design; material limitations may affect long-term margins; parafunction control not reported.	Ceramic fractures (10.6%) and chipping (2.3%) were the most frequent complications	[321]
Inlays, Onlays	Feldspathic porcelain and other glass-based ceramics	SR/MA	I	3266 restorations (Glass ceramics: 2218 + Feldspathic: 1048) - 10-year follow-up: 2904 restorations (Glass ceramics: 1075 + Feldspathic: 1829)	Up to 10 years	Posterior	- 5-year follow-up: (Glass ceramics: 92% Feldspathic: 90%)- 10-year follow-up: (Glass ceramics: 89% + Feldspathic: 91%)	~3–9% (cumulative)	Pooled protocols and outcomes; survival evaluated at 5 and 10 years with variable criteria.	Fractures (6.2%), endodontic problems (3%), secondary caries (1.7%), and debonding (0.9%)	[322]
Inlays, Onlays	Feldspathic porcelain, LR, LD	Prospective	III	5791 (4475—feldspathic porcelain, 1076—LR glass–ceramic, and 240—LD)	Up to 15 years (Mean: 3 years)	Posterior	~84%	~3.8% (cumulative)	Multimaterial practice-based dataset; operator and indication variability limit comparability.	Ceramic or tooth fractures (44.5%), endodontic complications (16.4%), secondary caries (8.2%), postoperative sensitivity (3.2%), and periodontal complications (2.7%)	[323]
Inlays, Onlays, Overlays	LR and LD	SR/MA	I	605	10 years	Posterior	93%	9% (cumulative)	Mixed ceramics; adhesion and finishing details variably reported; mostly minor repairs.	Fractures/chipping (4%), followed by endodontic complications (3%), secondary caries (1%), and debonding (1%)	[324]
Inlays, Onlays, Crowns	Pressed LD (IPS e.max Press)	Clinical Study	III	2392 (1782— Crowns; 610—Inlays, Onlays)	16.9 years	Posterior	96.49%	0.92% (cumulative)	Practice-based network study; high external validity but protocol adherence varied across centers.	Bulk fracture or large chip	[298]
Inlays	Pressed LD glass–ceramic (IPS e.max)	Clinical Study	III	246	> 9.9 years	Posterior	93.9%	1.22% (cumulative)	Posterior molar-only cohort; occlusal schemes and parafunction not detailed.	Bulk fracture or large chips, all in posterior molars	[297]
Inlays	LD	Retrospective	III	29	8.3 years	Posterior	100%	0%	Small retrospective series; selection bias possible; cement protocol not fully specified.	-	[295]
Inlay, Partial Crown, Crown	LD (IPS e.max Press)	Retrospective	III	250 (inlay— 66; partial crown—174; crown—5)	8.5 years	Posterior	94%	83.8% (cumulative)	Undergraduate clinic data; technique variability across operators.	Fracture (2%), Debonding (0.4%), Endodontic (0.8%), Caries (0.8%)	[325]
Partial crowns	LD	Retrospective	III	114	8.3 years	Posterior	95%	Technical (2.7%), esthetic (1.8%), and biological (5.3%) (cumulative)	Mixed substrates and preparation designs; maintenance protocols not reported.	Debonding (0.9%), marginal staining (1.8%), secondary caries (2.6%), irreversible pulpitis (1.8%), and tooth loss (0.9%)	[295]
Crowns	IPS Empress 2	Prospective	III	27	5 years	Posterior	100%	0%	Small prospective cohort; posterior-only; limited statistical power.	None observed	[326]
Crowns	LD (IPS e.max Press, IPS e.max CAD, IPS Empress 2)	SR	I	696	Up to 10 years	Posterior, Anterior	100% at 2 years, 97.8% at 5 years, and 96.7% at 10 years	~1.3% (cumulative)	Pooled crown cohorts; monolithic/veneered distinction inconsistently reported; endpoint criteria variable	Core ceramic fractures (~0.7%) and veneering chipping (~0.6%), mostly occurring in the posterior region, while endodontic issues, secondary caries, and debonding	[103]
Crowns	LD (IPS e.max)	Clinical Study	III	22 (conventional veneered crowns), 22 (reduced-thickness monolithic crowns)	1 year	Posterior	100% veneered crowns, 95.5% monolithic crowns	0% veneered crowns, 4.5% monolithic crowns (cumulative)	Short-term comparison; small sample; limited inference for long-term posterior use.	Catastrophic fracture (occlusal surface, required replacement)	[271]
Monolithic and Bilayered Crowns	LD (IPS e.max)	Clinical Study	III	1960	Up to 10.4 years	Anterior, Posterior	Monolithic: 96.5% at 10.4 years Bilayered: 100% at 7.9 years	Monolithic: 0.21% Bilayered: 0% (annually)	Mixed clinical settings; tooth-type and load stratification partial; good external validity	Fracture (bulk or large chip requiring replacement), Minor chips noted but did not require replacement unless significant	[304]
Crowns	LR	Clinical Study	III	93	Up to 15 years	Anterior, Posterior	79.6%	20.4% (cumulative)	Older-generation material; very long follow-up; higher event rate reflects material and indication era.	Fractures/chipping (5.4%), periodontitis (4.3%), occlusal wear	[305]
Crowns	LD	SR	I	~1500+	Up to 15 years	Anterior, Posterior	87.1–100%	<1%–16.6% (cumulative)	Pooled across indications and designs; heterogeneous reporting of success vs. survival.	Fractures of the crown or core (~1–3%), veneer chipping in bilayered restorations (2–5%), loss of retention (1–4%), need for endodontic treatment (2–3%), gingival inflammation (~2–5%), marginal caries (<1–2%), and debonding or dislodgement (~1–3%).	[313]
Bridges (3-unit)	IPS Empress 2	Prospective	III	31	5 years	Anterior, Posterior	70%	19.4% (cumulative)	Early-generation framework; connector stress and span length limit longevity.	Framework fractures (9.7%), biological failures (6.5%), and an irreparable partial veneer fracture (3.2%).	[326]
Bridges	LD (Mainly IPS e.max Press, IPS Empress 2)	SR	I	145	Up to 10 years	Posterior	83.3% at 2 years, 78.1% at 5 years, and 70.9% at 10 years	17.2% (cumulative)	Posterior spans pooled; connector and load variability across studies.	Core/framework fractures, veneering ceramic chipping, debonding, endodontic issues, and secondary caries	[103]
Bridges (3-unit)	LD (IPS e.max Press)	Clinical Study	III	33	Up to 8 years	Anterior, Posterior	93%	6% (cumulative)	Small single-material cohort; connector dimensions and indication limit generalizability.	Fractures requiring replacement (6%), chipping of the veneering ceramic (6%), loss of retention requiring recementation (6%), and endodontic complications in abutment teeth (3%)	[311]
Bridges (3-unit)	Monolithic CAD/CAM LD	Multicenter	III	32	10 years	Anterior, Posterior	84.4%	15.6% (cumulative)	Multicenter design; endpoint heterogeneity and maintenance protocols vary across sites.	Connector fracture (3.1%), repeated debonding (3.1%), persistent pain (6.2%), abutment loss (3.1%)	[312]
Bridges (3-unit)	LD	SR	I	~270+	Up to 15 years	Anterior, Posterior	48.6–100%	2.7–46% (cumulative)	Wide indication mix; high heterogeneity	Fractures at the connector or pontic area (3–10%), loss of retention or debonding (4–6%), persistent or post-operative pain (2–5%), endodontic complications in abutment teeth (2–3%), chipping of veneering ceramic (2–6%), and biological complications such as periodontal issues or marginal inflammation (~2–4%)	[313]
Bridges	LD (IPS e.max, Empress)	Integrative Review	I	35	Up to 6 years	Anterior	100%	0%	Small sample	None observed	[314]

Abbreviations: EV, evidence level; SR/MA, systematic review/meta-analysis; LD, lithium disilicate; LR, leucite-reinforced; NR, not reported.

The clinical evidence indicates that LD is the most reliable glass-based ceramic, offering a strong balance between esthetic excellence and long-term mechanical performance. Extensive prospective cohorts and meta-analyses consistently report survival rates above 95–97% at 5–10 years, confirming its stability across a variety of restorative indications. By contrast, feldspathic and leucite-reinforced (LR) ceramics, although capable of unmatched translucency, show greater susceptibility to surface chipping, marginal wear, and color instability over time. These differences illustrate a fundamental trade-off in glass ceramics: the pursuit of optical perfection often occurs at the expense of mechanical robustness and maintenance-free longevity. For veneers, LD demonstrates excellent predictability, maintaining near-perfect survival at ten years with minimal technical or biological complications [286,317,318]. This reliability is closely linked to etch-and-silane bonding and predominantly enamel-based preparations, which permit ultra-thin restorations (≈0.3–0.5 mm) with stable adhesion [278,284]. In contrast, feldspathic and LR veneers perform well esthetically but accumulate more minor events such as chipping and marginal discoloration, particularly when dentin bonding or suboptimal cementation techniques are used [286,315,319]. These findings emphasize that the adhesive interface, rather than intrinsic strength alone, governs the long-term outcome of thin glass–ceramic restorations.

For inlays and onlays, LD remains the benchmark for adhesive restorations, achieving approximately 94–98% survival over 8–17 years even under bruxism or high-load conditions [295,296,297,298]. The material’s strong micromechanical coupling with enamel and dentin allows conservative preparation designs while maintaining resistance to fatigue and crack propagation [301,302,303]. Large multicenter data confirm similar results, with a reported 96% survival after almost 17 years in practice-based settings [298]. In comparison, feldspathic and LR systems perform acceptably in low-stress regions but show higher rates of marginal breakdown and fracture in posterior sites [321,324].

For crowns and short-span fixed partial dentures (FPDs), LD provides consistent success, with 5–10-year survival above 95% and low annual failure rates [103,304,313]. The material’s intermediate toughness permits use in both anterior and posterior crowns when an adequate occlusal thickness (≈1.5–2.0 mm) is maintained, and even thinner monolithic designs perform well with proper occlusal control [270,271,272,302]. LD bridges limited to anterior or premolar sites show favorable outcomes (≈85–93% survival at 8–10 years) when connector geometry and load direction are optimized [311,312,313,314], though zirconia remains preferable for longer or posterior spans due to superior fracture toughness.

Although the evidence base is robust, differences in follow-up length, adherence protocols, and reporting criteria remain. Furthermore, many studies have been conducted in controlled academic environments, which may limit the direct applicability of their results to everyday clinical scenarios. The evidence, however, shows that when adhesive protocols and surface finishing are standardized, LD offers exceptional longevity, whereas feldspathic and LR ceramics, while esthetically superior, demand higher maintenance and case selectivity.

4.6. Challenges and Future Directions

Dental glass–ceramics generally exhibit lower flexural strength and fracture toughness compared to high-strength oxide ceramics like Y-TZP. Because of that, their mechanical strength can be insufficient for demanding applications, such as multi-unit posterior bridges. Increasing the crystalline content can boost strength, but often can also alter the translucency. Leucite glass–ceramics partially overcome this by matching the refractive index of the crystal and glass phases so that up to ~50 wt% leucite can be added with minimal opacity. Thus, balancing mechanical performance with natural-looking translucency is an ongoing challenge with these materials [12].

Like other dental ceramics, glass–ceramics are vulnerable to slow crack growth and chemical erosion in the oral environment. Under repeated occlusal loading in humid conditions, subcritical cracks can gradually propagate, leading to strength degradation over time [327,328]. The humid oral conditions cause stress corrosion cracks at the tips, which accelerate crack growth, occurring below 50% of the initial strength. Lithium disilicate and leucite-based glass ceramics have shown susceptibility to such stress corrosion and fatigue, which can compromise their long-term stability [102]. Furthermore, the acidic and alkaline conditions in the mouth also pose a risk of surface corrosion. Dental glass–ceramics should be in accordance with the solubility limits specified by ISO 6872, which sets a maximum 100 μg/cm³ for single-unit restorations to minimize chemical degradation and ensure long-term clinical performance [329,330]. If the glass ceramic is not sufficiently resistant to oral acids and abrasion, surface degradation in the form of wear or gloss loss may also occur. Even though formulations are usually stable, it can be difficult to maintain polish and stop microscale corrosion after years of exposure for glass–ceramic restorations with exposed glassy matrix phases [331,332,333]. A major advantage of glass–ceramics is their ability to etch their silica-based glass matrix with hydrofluoric acid and bond them to tooth structures with resin cements. While this adhesive bonding improves retention and helps reinforce brittle ceramic, the durability over longer periods can be affected. Bond strength of resin-cemented glass–ceramics tends to decrease under thermal cycling and water storage due to hydrolytic degradation of the resin and silane interface. In Vitro findings have shown significant drops in bond strength after one month of water storage and thermocycling [334]. Additionally, a mismatch in thermal expansion between the ceramic and the resin cement/tooth structure can induce stresses at the interface. Although adhesive bonding is an effective technique for glass–ceramics, there are certain factors, like resin water sorption, optimal curing, and stable silane coupling, that can influence the durability of these materials over time. Ongoing improvements in ceramic primers and cements are aimed at preserving high bond strengths over time [335,336,337,338,339].

The most commonly used method to fabricate glass–ceramics restorations is CAD/CAM milling of prefabricated blocks. While this technique is convenient, it also poses some downsides. Machining a crystalline glass–ceramic is abrasive to tools, leading to rapid diamond bur wear. Hard ceramics can also suffer edge chipping during milling, especially at sharp margins, if the material is brittle or contains large crystals. High-strength ZrO₂-reinforced lithium silicate glass–ceramic is considered to be the most difficult to machine due to exhibiting high cutting forces and frequent chipping, making consistent fabrication a technically challenging [12,340,341,342]. Another limitation of CAD/CAM is material wastage, as up to 90% of the original block can be cut away [248]. This not only increases cost but also contradicts sustainability goals. Furthermore, milling pre-crystalized or partially sintered glass–ceramics makes the process more complex, as it requires a final crystallization firing step. Additive manufacturing (3D printing) of ceramics is becoming a choice, but current 3D-printed dental ceramics often have lower density and accuracy, requiring post-sintering that can cause shrinkage and defects. Thus, producers currently have to deal with material waste, tool wear, and microcracks caused by milling [12,234,248,343,344,345,346,347]. Overcoming these manufacturing issues, either by improving machinability (via microstructure control) or by adopting new fabrication methods, is essential to fully exploit glass–ceramics in custom dental applications. However, fully integrating 3D printing into dental ceramics will require surmounting fundamental reliability challenges. Printed restorations tend to contain more internal flaws (e.g., porosity, layer lines), resulting in a broader flaw population and a notably lower Weibull modulus (i.e., lower structural reliability) compared to conventional milled ceramics. Even if mean flexural strengths approach those of milled parts, the greater scatter in strength of printed glass–ceramics (often reflected in Weibull moduli in the single digits) remains a barrier for widespread adoption in high-stress applications. Moreover, ensuring a dense, phase-pure microstructure in a 3D-printed glass–ceramic is challenging; factors like binder removal, non-uniform shrinkage, and crystallization kinetics can introduce unintended phases or residual porosity that weaken the material. These issues highlight the need for improved printing formulations and post-processing to achieve the consistent quality needed for critical restorations [348].

Future perspectives for dental ceramics include refining the microstructure, innovating manufacturing techniques, expanding clinical applications, and offering materials with biological functionality. A promising route to address strength-toughness-translucency related problems is engineering glass–ceramics with nanometer-scale crystalline phases. Reducing crystal size from the conventional micrometer scale to the nanometer range can result in nanocrystalline glass–ceramics with remarkable properties. For example, in lithium-disilicate glass–ceramic, the average length of rod-like Li₂Si₂O₅ crystals is 3–6 μm. With the right technique, this crystal size can be reduced to the point of achieving a needle-like form, which makes them stronger and tougher, with higher translucency. Moreover, if this nanocrystal is interconnected to form a 3D architecture, it can achieve even an ultrahigh strength (e.g., ZrO₂-SiO₂) [12]. Fu et al. achieved a 3D interconnected nanoarchitecture by embedding tetragonal ZrO₂ nanoparticles in a silica glass matrix with a final flexural strength of 1014 MPa (the highest reported among glass–ceramics [345,346]. These nanostructured glass ceramics use nanoscale toughening methods like fracture deflection and interfacial bridging to transfer stress more efficiently between the stiff crystalline phase and the compliant glass matrix. The development of nanoengineered glass–ceramics, possibly through methods like controlled nucleation or sol–gel routes, is a key future direction in the production of a newer generation of restorative dental materials that fulfill both strong and esthetic demands [12,345,346].

To overcome limitations of conventional milling, attention has been directed towards additive manufacturing. Techniques such as stereolithography, direct inkjet printing, and selective laser sintering have already been explored for ceramics, but applying them to glass–ceramic systems is still in the early stages. One future direction might be towarded hybrid manufacturing, which combines 3D printing with CNC milling. In an HM workflow, reduced material waste and a complex geometry can be achieved, as a near-net dental prosthesis could be 3D-printed. Then, it can be minimally milled to obtain a high precision fit and surface finish. Therefore, a hybrid process could address the current issues of 3D printing, such as insufficient dimensional accuracy and shrinkage upon sintering [12,347,348,349,350,351,352]. Gailevičius et al. have demonstrated the feasibility of 3D printing a ZrO₂–SiO₂ glass–ceramic via ultrafast laser nanolithography, with feature resolution of 100 nM after heat treatment. However, scaling up these methods is still quite difficult, though, as printed parts frequently need post-debinding and sintering, which can cause porosity and cracking. Consequently, today’s printed glass–ceramic parts often exhibit a lower reliability than milled ones due to these microstructural flaws. Ongoing research is focusing on optimizing ceramic slurries/inks (to control viscosity and maximize particle loading), improving printer resolution to obtain denser microstructures, and refining sintering protocols to minimize distortion and residual porosity. In the coming years, these advances aim to produce more consistent, high-density 3D-printed glass–ceramic restorations. If durability and precision can reach parity with milled ceramics, additive techniques may enable the routine production of multi-unit prostheses or patient-specific designs with minimal waste and labor [12,17,347,353,354].

One future vision is to extend the use of glass–ceramics, even in dental implants and abutments. Currently, implants are made almost exclusively of titanium or zirconia. However, a strong bioactive glass–ceramic implant could offer superior esthetics while eliminating the risk of metal allergies. Nanocrystalline composites can be a future candidate for ceramic implants and abutments or even for multi-unit bridges and full-arch prostheses [12]. Another approach to impart bioactivity is applying surface coatings of osteoconductive materials (such as hydroxyapatite or bioactive glass) onto high-strength ceramic cores. This could, in theory, combine the structural strength of core ceramics with the bone-bonding capability of bioactive coatings; however, the long-term stability of such coating–ceramic interfaces under cyclic oral loads remains a significant concern. Mismatches in thermal expansion or stiffness between the coating and the ceramic can generate residual stresses, and under repeated chewing forces, the coating may develop micro-cracks or even delaminate over time. To address this, functionally graded interfaces and nanostructured bonding layers are being explored to improve adhesion and distribute stress more evenly. While these strategies show promise in laboratory studies (e.g., improving interfacial toughness and fatigue resistance), robust In Vivo validation is required to ensure that bioactive coatings can endure years of service without degradation [355].

One thrilling direction for dental materials is the development of bioactive glass–ceramics that do more than just restore the lost structure. Thanks to their glassy matrix, these materials can be chemically modified to include functional ions like calcium, strontium, magnesium, and phosphorus. When implanted, these ions can gradually release into surrounding tissues, promoting bone bonding and soft tissue integration. In addition, antibacterial ions like silver and copper can be incorporated to offer the material antimicrobial properties, helping to reduce the risk of peri-implantitis or recurrent decay at restoration margins. Mechanistically, the release of calcium and phosphate ions from a bioactive glass–ceramic facilitates the formation of a bone-like hydroxyapatite layer on its surface, creating a tenacious chemical bond with the host bone [356]. Strontium (Sr²⁺) ions play a dual role: they stimulate osteoblast activity while inhibiting osteoclasts, thereby enhancing new bone formation and increasing local bone density around the implant site [357]. Magnesium additions can further aid bone tissue response by supporting mineralization and improving the quality of the regenerated bone. Meanwhile, the bactericidal effect of silver and copper ions arises from their sustained release into the oral environment, where they penetrate microbial cell walls and disrupt vital enzymes and DNA, leading to broad-spectrum antibacterial action [358]. By harnessing these ion-release behaviors, next-generation glass–ceramics could transform a dental restoration from a passive replacement into an active contributor to oral health, simultaneously reinforcing the tooth, integrating with the tissue, and fighting bacteria. Overall, the integration of therapeutic functionalities into glass–ceramics marks a promising step toward next-generation dental materials. By combining mechanical reliability with targeted biological activity, they could have the potential to shift dental restoration from passive replacements to active contributors in oral health and tissue regeneration [359].

In conclusion, solving the above challenges is essential to further development and clinical success of dental-glass ceramics. New ideas on how to improve material composition and their processing will make it possible to create stronger, more reliable, and durable glass–ceramics. For instance, defect-free additive manufacturing workflows and interface-engineered bioactive surfaces represent two avenues to significantly improve performance and longevity. These strategies could expand the applications of these materials, bringing them closer to an ideal restorative that is strong, durable, biologically interactive, and exhibits a lifelike appearance.

5. Discussion

This review synthesized extensive scientific and clinical evidence on zirconia- and glass-based ceramics, providing a unified understanding of how both material classes function in restorative dentistry. By presenting their composition, microstructure, mechanical and optical behavior, biocompatibility, and clinical applications in parallel, this review consolidates a wide body of data that is typically presented in fragmented or material-specific publications. The analysis across these domains highlights that zirconia and glass–ceramics are not interchangeable materials, but rather complementary systems whose suitability depends strongly on clinical indication, mechanical demands, esthetic requirements, and bonding considerations.

A central contribution of this article is addressing the gap created by the literature that evaluates zirconia or glass–ceramics separately. As demonstrated throughout the manuscript, zirconia excels in transformation-toughened strength, resistance to bulk fracture, and performance under high posterior loads, whereas glass–ceramics, particularly lithium disilicate, remain unmatched in optical fidelity and adhesive bonding. Yet much of the available literature focuses on one material class at a time, creating barriers for clinicians who must evaluate both categories when making restorative decisions. By analyzing these materials side-by-side, this review clarifies where their functional domains diverge and where modern formulations, such as high-translucency zirconias or zirconia-reinforced lithium silicates, begin to overlap. This integrated perspective more accurately reflects the way restorative materials are selected in daily clinical practice.

Interpretation of the compiled evidence reveals consistent patterns. Zirconia shows the strongest clinical support for single crowns, both tooth- and implant-supported, with high survival and relatively low complication rates. Its mechanical reliability is especially advantageous in high-load posterior areas. Conversely, glass–ceramics demonstrate exceptional long-term success in adhesively bonded veneer, inlay–onlay, and anterior crown applications, where esthetic integration and conservative preparations are paramount. Lithium disilicate, in particular, shows excellent durability when adhesively bonded and used within its recommended thickness and indication boundaries. These findings emphasize that optimal clinical outcomes depend not only on material selection but also on the restorative design, surface finishing, adhesive protocol, and load environment, factors repeatedly supported throughout the review’s evidence tables and technical sections.

The review also identifies several challenges that continue to shape the future development of both material classes. For zirconia, issues include LTD in some formulations, the strength–translucency trade-off in cubic-enriched systems, and variable bonding reliability due to its non-silica-based structure. Glass–ceramics face their own limitations, including susceptibility to fatigue, hydrolytic degradation of adhesive interfaces, and machinability constraints. Manufacturing innovations, such as high-speed sintering, graded zirconia architectures, nanocrystalline glass–ceramics, and emerging additive-manufacturing workflows, offer promising avenues to mitigate these limitations. However, as highlighted in the review, most of these advancements still require standardized testing, longer-term clinical validation, and improvements in processing reliability before they can be broadly adopted.

Several implications arise from this synthesis. Clinicians should prioritize zirconia for high-load or long-span restorations and select lithium disilicate or ZLS when bonding, optical demands, or minimally invasive preparation are key. Researchers and manufacturers, on the other hand, may benefit from the comparative data presented here to further refine composition–microstructure–property relationships, improve manufacturing reproducibility, and design biofunctional or nanostructured ceramics that transcend the traditional mechanical–esthetic trade-off. Importantly, the present paper underscores how ongoing innovations have begun to erode the historical boundaries between these two material families, suggesting that future restorative materials may integrate their respective advantages more seamlessly.

This review also carries inherent limitations. As a narrative review, it synthesizes a large but heterogeneous body of evidence that varies in study design, follow-up duration, testing methods, reporting criteria, and zirconia or glass–ceramic generation. Differences in cementation protocols, finishing techniques, clinical operator skill, and inclusion/exclusion of high-risk patients (e.g., bruxers) contribute to variability in reported outcomes. Furthermore, emerging technologies, such as additively manufactured ceramics, multi-dopant zirconias, and bioactive ceramic systems, are still supported primarily by In Vitro or early clinical data, limiting the ability to draw definitive long-term conclusions. Nevertheless, by consolidating and critically contextualizing these diverse findings, this review provides a comprehensive, clinically relevant foundation for understanding contemporary zirconia and glass–ceramic materials.

6. Conclusions

Zirconia and glass–ceramic materials have greatly advanced restorative dentistry by offering durable, esthetic, and biocompatible alternatives to metal-based restorations. Zirconia continues to perform exceptionally in situations that demand high strength and long-term stability, while glass–ceramics remain the materials of choice for esthetic, adhesive, and minimally invasive treatments.

There are limits to each type of material, but the evidence shows that when the material is chosen to meet the specific clinical needs of the restoration, reliable results can be achieved. Recent advancements in composition, microstructural design, and manufacturing methods have addressed persistent challenges, including aging behavior, strength–translucency trade-offs, and bonding difficulties.

Lately, emerging technologies show the potential for next-generation ceramics to offer improved performance and greater versatility. However, additional long-term clinical data are required to support these technologies and facilitate their incorporation into standard practice. As research continues, zirconia- and glass-based ceramics are expected to sustain and expand their pivotal role in promoting functional, stable, and esthetically integrated restorations in modern dentistry.